Full text of "Chemistry of the organic dyestuffs. By R. Nietzki. Translated, with additions"

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From the-vlibrary optKe late

w. hqdGsO^jl^lis

M.A.. M.B.. LL.D

)^^K^

The first Professor of Applied Chemistry

in the University of Toronto

and second

Dean of the Faculty of Applied Science
and Engineering 1914 to 191Q

Presented to the Department of CKemical

Engineering and Applied Chemistr?

\y^ Mrs. W. Hodgson Ellis,

Marck 7th, 1023

CHEMISTRY

OF THE

ORGANIC DYESTUFF8.

CHEMISTRY

OP THE

ORGANIC DYESTUFFS.

R. NIETZKI, Ph.D.,

PROFKSSOR AT THE UNIVERSITY OK BASLE.

TRANSLATED, WITH ADDITIONS, BY

A. COLLIN, Ph.D., and W. RICHARDSON.

LONDON :

GTJRNEY & JACKSON, 1 PATERNOSTER ROW.
fSuccEssoKS TO Mr. VAN VOORST.)

MDCCCXCII.

D. VAN NOSTRAND COMPANY,

KENV YORK.

LIBRA,, y, ^
OCT 1 2 1972 I

ysin OF w*^V

AXSBK Y FLAMMAM.

PBIHTED BY TAYLOR AKD PKAKCIB,
BED LION COURT, FLEET STREET.

AUTHOR'S PREFACE.

About three years ago I wrote an article for Ladenburg's
' Handworterbuch der Chemie/ containing in a concise form an
exhaustive account of the history of the Organic Dyestuffs. This
article was also published separately^ and its good reception
induced me to produce the present work, which I have based as
far as possible upon the earlier one.

The article in question was not complete in itself, and in the
present instance certain sections which came under other headings
in the ' Handworterbuch * have been added. New material has
also been supplied through the advances made in the coal-tar
colour industry and in our scientific knowledge of the constitution
of dyestuffs during the last three years. Again, some subjects
have been dealt with at a greater length than was permitted by
the somewhat limited space of the 'Handworterbuch.^ Conse-
quently, the subject-matter of the earlier work has been submitted
to a thorough revision, and the systematic classification of dye-
stuffs into natural chemical groups attempted in the original book
has been carried out in a more complete manner, owing to the
advances made in our knowledge of their constitution.

The present work cannot therefore be regarded as a second
edition of the article from the ' Handworterbuch,^ and as I have
sought to give the whole the form of a small chemical handbook,

Vi AUTHOR^S PRErACE.

dealing with dyestuffs from a scientific standpoint, I have selected
' The Chemistry of the Organic Dyestuffs ' as a suitable title.

In this work, as in the previous one, considerable weight has
been laid upon the relationships existent between the constitution
and tinctorial properties of the dyestuffs.

I have thought it advisable to deal only with the principles
involved in the manufacture of individual dyestuffs, as details for
their technical production are unreliable, owing to the continuous
developments taking place in the industry in question.

The application of dyestuffs to textile fibres has been dealt with
rather more fully than in the earlier work, but not at a greater
length than is in accordance with the character of the book. To
technologists requiring further details of the application of dye-
stuffs I can recommend HummePs excellent work on ' The
Dyeing of Textile Fabrics.''

Basle, October 1888.

TRANSLATORS' PREFACE.

Little remains for us to add to Prof. Nietzki's account of the
design and character of his book. It has met with very general
appreciation in Germany, and this made us think that a trans-
lation might be of service to English workers in the field . which
the book covers.

Some time has elapsed since the original appeared, and we have
attempted as far as possible to bring the subject-matter up to date.
New colouring-matters have been introduced without altering
Prof. Nietzki's method of classification, a method which has been
very generally adopted since its appearance. In some cases
(Primuline, Thioflavine ; Pyronine, &c.) new sections might have
been desirable ; we preferred, however, to leave the book in its
original form.

The figures in the text apply to the references given on pages
273-288. The references have been left as in the original, with
the one exception that, wherever possible, the English-Patent
number has been added.

Our thanks ai'c due to the Directors of the Farbwerke Hbchst
(Meister, Lucius, and Briining) and of the Farbenfabriken, vorraals
F. Bayer and Co., Elberfeld, for the ready kindness with which
they placed ample information at our disposal.

Paisley, May 1892.

CONTENTS.

Page

Iktboduction 1-22

Colour, 1 ; Chromophors, Chromogens, 3 ; Theory of dyeing, 4 ; Con-
stitution of chromogens, 7 ; Salt- forming groups, Auxochromic
groups, 12; Acid and basic dyestuffs, 14; Mordants, lakes, 15;
Dye-trials, 16 ; History of artificial colours, 17 ; Classification,
22.

CHAPTER I.

NiTRO-COMPOUNDS 23-27

General, 23 ; Picric Acid (Trinitrophenol), 24 ; Dinitrocresol, 24 ;
Dinitronaphthol, Dinitronaphtholsulphonic Acid, 25 ; Brilliant
Yellow, Tetranitronaphthol, Palatine Orange, Aurantia, Salicyl
Yellow, 26 ; Isopurpuric Acid, 27.

CHAPTER II.

AZO-DYESTDFFB 28-79

Introductory, 28-34.

I. Amidoazo-compounds 35-43

Amidoazobenzene, 35 ; Amidoazobenzenemonosulphonic Acid, 36 ;
Amidoazobenzenedisulphonic Acid (Acid Yellow), 36 ; Dimethyl-
amidoazobenzene, Dimethylamidoazobenzenesulphonic Acid, 37 ;
Phenylamidoazobenzene, Phenylamidoazobenzenesulphonic Acid
(Tropiiolin 00), 38 ; Amidoazotoluenebenzene, Amidoazo-
toluenes, 39 ; Amidoazoxylenes, 40 ; Diamidoazobenzeno (Chry-
soidine), 40 ; Parazoaniline, 41 ; Triamidoazobenzene (Bismark
Brown), 42; Benzeneamidoazonaphthalene, Amidoazonaphtha-
lene, 43.

X CONTENTS.

Page

II. OXYAZO-COMPOUNDS 44-59

Oxyazobenzene, Dioxyazobenzene, 44 ; Tropaolin 0, 45 ; Dioxyazo-
benzenes (Azophenols), 45.

Naphtholazo-dyes, constitution, 46 ; Naphtholsulphonic Acids, 48 ;
Azobenzene-a-naphthol, 53 ; Monosulphonic Acid (Orange I),
54 ; Azobenzene-/3-napbthol, Sulphonic Acids, 54 ; Disulpbonic
Acids, Orange G, CroceVn Orange, Scarlet 2 G, 55; Azo-dyes
from /3-naphtholdisulphonic acids, 55, 56 ; a-azonaphthalene-|3-
naphthol, Monosulphonic Acid (Eoccellene, Fast Ked), 57;
Disulpbonic Acids, Bordeaux B, Crystal Scarlet, Crocei'n Scarlet
3 Bx, Azorubin, 58 ; Silk-red, 59.

III. AZC-DYES FKOM DiAZO-CARBONIC AciDS 59, 60

Dimetbylamidobenzeneazobenzoic Acid, Pbenolazometabenzoic Acid,
Resorcinazobenzoic Acid, /3-naphtholazobenzoic Acid, 59.

IV. Azo-DYES EKOM CaRBONIC AciDS AND DlAZO-COMrOXTNDS .... 00-62

Azobenzenedimethylamidobenzoic Acid, Dimethylamidobenzoic Acid-
azobenzoic Acid, Azo-S-diamidobenzoicacid-p-benzenesulphonic
Acid, 60 ; Azobenzenesalicylic Acid, Azonaphthalenesalicylic
Acid, Dyes from Nitrodiazo-compounds and Salicylic Acid
(Alizarin Yellows), 61.

V. Teirazo- or Disazo-dyestuffs 62-74

Introductory, Phenoldisazobenzene, 62; Resorcinazobenzene, 63;
Azo-dyes from Amidoazo-compounds, 63 ; Benzenedisazobenzene-
/3-naphthol, Monosulphonic and Disulpbonic Acids, Biebrich
Scarlet, 64 ; Crocein Scarlets, Archil Brown, Wool Black, 65 ; Azo-
dibenzenephenylenediamine, 65 ; Azodibenzene toluylenediamine,
66; Table of dyes from Amidoazo-compounds, 66; Secondary
and Tertiary azo-dyes from Nitrodiazocompounds, 67.

Azo-dyes from Benzidine and analogous bases, 68-74.

Congo Red, 68 ; Sulphonic Acids of a- and /3-naphthylamine, 69-
70 ; Azo-blue, Benzazurine, Tetrazostilbenedisulphonic Acid,
71; Table of direct dyes, 72, 73, 74; Azarin S, Sun YeUow,
Thiotoluidines (Primuline), 75 ; Erica, Thioflavine, 76 ; Direct
production of Azo-dyes on the fibre, 77 ; Diamine Blacks, 79.

CONTENTS. XI

CHAPTER in.

Page
OXTfttriNONES AND QTriNOlTEOXIMES 80-95

Introductory, 80 ; Naphthazarin, 81.

Anthraquinone-dyestuifs, 81-92.

Alizarin, 82 ; Constitution, formation, properties, 83 ; Technical
production, 84 ; Application, Turkey lied, 86 ; Nitroalizarin,
87 ; Trioxyanthraquinones, Purpurin, 87 ; Iso- (Anthra-) pur-
purin, Flavopurpurin, 88 ; Anthragallol, Alizarin Bordeaux
and Cyanines, 89 ; Alizarin Blue, 91 ; Alizarin Indigo-blue
S and Green, 92 ; Styrogallol, 92.

Quinoneoximes, 93-95.

Introductory, Dinitrosoresorcin, 93 ; Fast Green, 94.

Naphthaquinoneoximes, 94 ; Gambine R & G, Naphthol Green,
Dioxine, 95.

CHAPTER IV.

Kbtoneimides and Htdrazides 96-101

Introductorj', 96 ; Auramine, preparation, 98 ; salts, properties,
Phenyl- and Tolyl-auramine, 99 ; Phenylhydrazides, Tartrazine,
100.

CHAPTER V.

Triphentlmethane Dyestuffs 102-145

Introductory, 102 ; Formation, 104.

A. Bosaniline Dyestuffs 105-131

Tetramethyldiamidotriphenylcarbinol (Malachite Green), 106 ; Salts,
derivatives, preparation, 107; Nitro-derivative, 108; Dichlorte-
tramethyldiamidotriphenylcarbinol (Victoria Green 3 B),
Tetraethyldiamidotriphenylcarbinol (Victoria Green), Sul-
phonic Acids, Helvetia Green, 109 ; Light Green S, Quinoline
Green, 110 ; PararosanUine, 111 ; Methyl Violet, 112; Manu-

XU CONTENTS.

Page
facture, 113; Properties and composition, Acid Violets, 114;
Hexamethjlpararosaniline (Crystal Violet), 115 ; Hexaethylpara-
rosaniline (Ethyl Purple), Azo-Green, Methyl Green, 116; Rosani-
line Magenta), 118 ; Formation, 119 ; Base, 120 ; Salts, Sulphonic
Acids (Acid Magenta), Tetrabromrosaniline, 121 ; Trimethyl- and
Tetramethylrosaniline, Pentamethylrosaniline (Iodine Green),
Hexamethylrosaniline, 122 ; Triethylrosaniline (Hofmann's
Violet), 123; Tetraothylrosaniline, Acetyl, Triacetyl-, and
Tribenzoylrosaniline, 123 ; Magenta residues, 123 ; Aniline Blue,
124 ; Manufacture, 125 ; Monophenylrosaniline, 125 ; Diphenyl-
and Triphenylrosaniline (Aniline Blue), 126 ; Sulphonic Acids
of Aniline Blue, Alkali Blue, Water Blue, Cotton Blue, 126,
127; Diphenylamine Blue, 128; Aldehyde Green, 128; Di-
phenylnaphthylmethane dyestuflPs, Victoria Blue B, 130 ; Night
Blue, 131.

B. Bosolic Acid Dyestuffs 131-135

Introductory, 131 ; Aurin (Pararosolic Acid), Bosolic Acid, 132 ;
Pittacal, Eupittonic Acid, 133; Hexamethoxylpararosaniline,
134 ; Aurintricarbonic Acid (Chrome Violet), 134 ; Dyestuifs
from Benzotrichloride and Phenols, 135; Resorcin-benzein,
Bosamines, 135.

C. Phthaleins 136-143

Constitution, 136 ; Phenolphthalein, 138 ; Fluorescein, Eosin, 139 ;
Ethers of Eosin, 140 ; Spirit Eosin, Iodine derivatives of
Fluorescein, Lutecienne, Erythrosine, 141 ; Phloxiue, Bose
Bengal, 142; Bhodamine, 142; Pyronines, 143; Gallem and
Ccerulein, 144 ; Glycereins, 145.

CHAPTER VI.

QuiNONEiMiDE Dyestupfs 146-168

Introductory, 146.

1. Indamices 149-161

Phenylene Blue, Tetramethylindamine, 149 ; Toluylene Blue, 150.

2. Indophenols 151-153

Preparation, properties, 151 ; Application, 152.

CONTENTS.

3. Indamines and Indophenols containing Sulphur .... 153-161
Introductory, 153 ; Lauth's Violet, 155 ; Methylene Blue, 155 ;

Imidothiodiphenylimide, 158; Thionolines, Oxythiodiphenyl-
imide, Thionol, 159 ; Methylene Red, 160 ; Methylene Green, 161.

4. Oxyindamine and Oxyindophenols (Oxazines) 161-165

Naphthol Blue (Fast Blue), 161 ; Muscarine, 162 ; Nile Blue, Gallo-

cyanine, 163; Gallanaine Blue, 164; Prune, 165.

5. Dichromes 165-168

Resorufin, 165 ; Resazurine, 167 ; Orcirufin, 168.

CHAPTER VII.
A/JNE Dyestfffs 169-191

Constitution and formation, 169.

1. Eurhodines (Amido-azines) 172-174

2. Eurhodols (Oxy-azines) 175

3. Toluylene Red 175, 176

Toluylene Violet, Neutral Violet, 176.

4. Saffranines 177-189

Introductory, 177 ; Manufacture, 180 ; PhenosaflFranine, 181 ; Diazo-

compounds, 182; a- and /S-dimethylphenosaffranine, Tetrame-
thylphenosaffranine, Diethylsaffranines, 183 ; Acetyl and diazo-
compounds of Diethylsaffranines, 184 ; Tetraethylphenosaffra-
nine, 185; Tolusaffranine, 185; Methoxysaffranines, 186;
Neutral Blue, 187 ; Saffranol, 187 ; Indazine M, Basle Blue,
188 ; Azine Green, 189.

5. Magdala Red 189

6. Mauveine 190, 191

CHAPTER VIII.
Aniline Black 192-199

Formation, 192; Properties, 193; Constitution, 194; Technical
Aniline Black, applications, 197.

CHAPTER IX.
Indttlines akd Nigrosines 200-206

Formation, 200 ; Azophenine, 201 ; Indulines B, 3 B, and 6 B, 202
Soluble Indulines, 203 ; Nigrosines, 204 • Applications, 205 ;
Rosindulines, Azocarmine, 205 ; Fluorindines, 206.

XIV CONTENTS.

CHAPTER X.

Page

Qttinoline and AcRiDiNE Dtestuffs 207-218

Cyanine, Quinoline Red, 208 ; Quinoline Yellow (Quinophthalon),
209; Flavaniline, 210; Berberine, 212; Chrysaniline, 212;
Salts and derivatives, 213; Chrysophenol, 214; Synthesis of
Chrysaniline, 214 ; Acridine Yellow, Acridine Orange, Benzo-
flavine, 216.

CHAPTER XI.

Indigo Dyestuffs 219-241

Indol, 219 ; Indoxyl, 220 ; Lidoxylic Acid, Oxindol ; Dioxindol,
221 ; Isatin, 222 ; Isatic Acid, 223 ; Isatogenic Ether, Diisa-
togen, Indoxanthic Ether, Indigo Blue, 224 ; Preparation and
properties of Indigo-blue, 225 ; Dibenzoyl-indigo, Indigo-white,
226; Indigo- sulphonic Acids, 227; Application of Indigo in
dyeing, 228 ; Indigo-dicarbonic Acid, Indoine, 229 ; Indigo-
purpurin, Indirubin, Indigo-red, 231 .

Synthesis of Indigo-blue 231-236

From Indol and from Isatin, 231 ; Orthonitrophenylpropiolic Acid,
232 ; Synthesis from Orthonitrobenzaldehyde, 233 ; from Ben-
zylidene-acetone, 234 ; from Bromacetanilide and from Phenyl-
glycocine, 235 ; Synthesis of Indigo-disulphonic Acid, 236.

Constitution of the Indigo-group 236-241

CHAPTER XII.
Etjxanthic Acid and Galloflavine 242-246

Euxanthic Acid, Purree, 242 ; Euxanthone, 243 ; Derivatives and
constitution, 244.

Synthetical Oxyketone Dyestuffs 245

Trioxybenzophenone (Alizarin Yellow A), GaUacetophenone (Ali-
zarin Yellow G), 245.

EUagic Acid, 245 ; Galloflavine, 246.

CHAPTER XIII.
Canakine , , , 247

CONTENTS. XV

CHAPTER XrV.

Page
MXTBEXIDE 248

CHAPTEll XV.

DrESTUFFS OF UNKNOWN CoNSTITTTTION 249-271

Introductory, 249 ; Hsematoxylin, Hsematein, 251 ; Brazilin, 252 ;
Brazilein, Morin, 253 ; Young Fustic, Quercitrin, 254 ; Quer-
citin, 255 ; Rutin, Xanthorhamnin, Rhamnetin, 256 ; Luteolin,
257 ; Bixin, 258 ; Chrysin, Curcumin, 259 ; Carotin, Orchil and
Litmus, 260 ; Carthamin, 262 ; Santalin, 263 ; Alkannin, 263 ;
Crocin and Crocetin, Lokao (Chinese Green), 264; Cochineal,
265 ; Carmine Red, 266 ; Carmine, 267 ; Lac-dye, 269 ; Tyrian
Purple, 269; Catechu, 270; Cachou de Laval (Fast Grey),
271.

References 273-288

Appendix . . . f 289-306

Lndex 307-313

ERRATA.

p. 9. Phenaiine formula, read

instead of

P. 41. For Symmetrical Amidoazobenzene read Symmetrical Diamidoazobenzene.
P. 54. line 22, for Tropaolin OOO No. 1 read Tropaolin 000 No. 2.
P. 134. Formula for Chrome- Violet should be

/CgH3(0H)C00H
C-08H3(OH)COOH
I \OeH3OOOH
O^

iufitead of

/OeH3(OH)COOH

OH— 0-C8H3(OH)COOH

\06H3(OH)COOH

P. 136. Bosamine formula should be

0106H3-N(CH3),

C,H3N(CH3),C1

insteaid of

rcoH,

■ OeH3N(CH3),

C6H3(CH3),01

INTEODIJCTION.

Certain clieraical bodies possess the property of only transmitting
or reflecting certain constituents of white lights while the others
are absorbed. In other words^ such bodies have a particular
colour, more or less characteristic. These bodies occur amongst
the so-called chemical elements, and the colour of the same element
may be totally diflPerent according to the form and state of aggre-
gation under which it is observed. Certain elements (e.g. chro-
mium) always form coloured compounds ; with others, again,
the coloration of the compounds may be regarded as an exception,
and if not caused by combination with a colour-giving element,
depends on the constitution of the compound.

Coloured carbon compounds come under the latter classification.

The number of organic compounds containing, besides carbon,
hydrogen, oxygen, and nitrogen is very large, and by far the greater
number of them are colourless. On the other hand, some compounds
of carbon with these elements possess colour which far surpasses
that of any other element, both as regards intensity and character.

The coloured carbon compounds often differ little, or not at all,
from the colourless ones in their percentage composition, and it is
this fact which renders it certain that it is the structure of the
compounds which causes in one case colour, in the other none.

In the life-processes of plants and animals both colourless and
coloured carbon compounds are formed, and the latter have been
employed since the earliest periods as dye-materials.

2 INTRODUCTION.

Natural dyestuffs have for many years been the subjects of
thorough chemical investigation, but their study has afforded little
knowledge as to the general nature of coloured carbon compounds ;
and it is only since dyestuffs have been prepared synthetically
that we have gradually come to understand the constitution of the
greater number of these bodies.

Very little is known of the primary cause of colour in such
compounds, but our knowledge is so far advanced that colour
is regarded as a characteristic property of whole classes of
chemical compounds ; and the study of the constitution of such
compounds has shown that a close relationship exists between
their colour and their chemical structure.

A study of the carbon compounds shows that compounds of
carbon with one or with several elements of equal valency are all
colourless. For example, all hydrocarbons are colourless, and
derivatives obtained by the introduction of monatomic elements
are also colourless.

Colour in coloured compounds depends on the introduction of
compound radicals, mostly polyvalent ; but at the same time a
certain building-up of carbon atoms in the molecule is necessary
for production of a real colouring-matter. For the latter reason,
nearly all organic dyestuffs belong to the aromatic series, and are
derivatives of benzene, naphthalene, anthracene, or quinoline.
The radicals which possess this power of producing colour in a
hydrocarbon show a characteristic behaviour towards nascent
hydrogen.

Nascent hydrogen possesses the property of converting coloured
carbon compounds into colourless ones with. greater or less facility ;
the reaction which takes place may, however, be widely different
in various cases. The nitro-group is converted into an amido-
group, and on oxidation the nitro-group cannot be reproduced.
The azo-group is converted in a similar manner into two amido-
groups, but as an intermediate stage of the reaction hydrazo-
compounds are formed.

These hydrazo-compounds may be regarded as types of a class
of colourless bodies, termed leuco-compounds. A large number

INTRODUCTIOX. 3

of dyestufFs yield these leuco-compouiids on reduction. These
new bodies mostly contain two atoms of hydrogen more than the
dyestufis, and are converted into the latter on oxidation.

This circumstance was made a subject of study by Graebe and
Liebermann (Ber. i. p. 106) ; and in 1867 a theory was advanced
assuming the presence of a bond between the colour-giving groups
in dyestuffs yielding leuco-compounds^ corresponding to the linkage
of the oxygen atoms in quinone in the constitutional formula
accepted at that period. In 1876 Otto N. Witt published a more
complete theory of the nature of colouring-matters, and this
theory may be comprised in the following general laws (Ber. ix.
p. 522).

The colour of a compound depends on the presence of a certain
group of atoms, which is therefore termed a colour-giving group
or chroqiophor.

The introduction of this chromophor produces a more or less
intensely coloured body, which, however, is not a dyestuflf; and
the dyestufFs are only formed by introduction of one or more
radicals capable of imparting salt-forming properties, which may
be acid or basic. Witt terms compounds which only contain a
chromophor, chromogens.

Before proceeding it is necessary, however, to define the differ-
ence between a coloured body and a dyestuff somewhat more
clearly. A real dyestuff is a body which possesses, besides colour,
the property of communicating colour to fibres, especially to
animal fibres, doing this by reason of a certain peculiar affinity
betwixt the colouring-matter and the fibre. If a silk skein is
placed in a solution of dyestuff, it gradually becomes dyed, while
the liquid, if not too concentrated, finally loses the whole of its
colour.

The property of dyeing belongs principally to compounds
possessing a more or less marked acid or basic character. It is
probable that these properties depend, at least in many cases, on
a partly basic, partly acid character inherent in the fibre, which
in the one case is developed by the colour-acid and in the other by
the colour-base.

4 INTRODUCTION.

The exact relationship between a fibre and a dyestuff is not
exactly known. Dyeing processes are usually divided into two
categories : adjective^ where the use of a mordant is necessary,
and substantive, where no third body is required to fix the dyestuff
on the fibre.

Two theories as to the nature of substantive dyeing have been
advanced, a chemical and a mechanical theory.

The chemical theory of dyeing supposes that a chemical com-
bination of dyestuff and fibre takes place, and this view is, to a
certain extent, supported by experimental proof, the researches of
Knecht in this direction being csper^ially worthy of attention.

According to the nature of a dyestuff, the fibre may act the
part of an acid or of a base : thus dyed fibres are compounds of
fibre and dyestuff constituted like salts.

For example, rosaniline is a colourless base, forming red salts.
If a skein of wool or silk be warmed in a colourless solution of
rosaniline, it becomes dyed red, and as completely as if a corre-
sponding amount of a salt of rosaniline had been employed. This
behaviour is easily explained if we assume that the fibre plays
the part of an acid, combining with the rosaniline to form a salt
which, like rosaniline salts, has a red colour. It may, however, be
observed that the red colour of rosaniline salts is only evident in
solution, and in the solid state these compounds have a more or
less marked bronze-green appearance. This point has been raised
by upholders of other theories, that were a salt of rosaniline and
fibre formed, it might naturally be expected to possess the green
colour of the solid salts of rosaniline.

If we regard dyeing operations as chemical processes, it is
probable, in applying salts of colour-bases, that these salts are
decomposed in the dyeing process, the fibre combining with the
base and the acid being set at liberty. Certain strong basic dye-
stulfs, such as methyl green, which (like all ammonium bases)
forms very stable salts, are not capable of dyeing wool directly. If,
however, ammonia is added to the dye-bath, the liberated colour-
base combines with the wool and dyes it green. Silk, on the other
hand, evidently possesses a stronger acid character than wool, as

INTRODUCTION. 5

it may be dyed with rncthyl green without any assistance. Knecht
has demonstrated by quantitative experiments that in dyeing wool
with the salts of basic colours, the acid in combination with the
colour-base is liberated during the dyeing process. For example,
if a solution of rosaniline hydrochloride (magenta) is treated with
wool till all colour is extracted, the hydrochloric acid which was
in combination with the rosaniline remains in the colourless bath.

The behaviour of some acid dyestutfs also supports the chemical
theory of dyeing.

As a rule animal fibres are not capable of decomposing the
salts of acid dyestuflfs, and in dyeing the colour-acids have to be
set at liberty by the addition of a stronger acid to the dye-bath.
Certain colour-acids, for example the sulphonic acids of amidoazo-
compounds, have a different colour to that of their alkali salts. In
dyeing wool with such colour-acids, the shade produced is that of
the salts and not that of the colour-acid, so that in such cases
wool evidently plays the role of a base.

In certain cases also there is evidence which points to the fact
that definite molecular combinations of dyestuff and fibre exist.

In dyeing processes, from a practical standpoint, a certain
quantity of dyestuff, seldom exceeding two per cent, of the weight
of the fibre, is found necessary to produce a maximum efifect as far
as shade is concerned. But this by no means expresses the limit
to the amount of dyestuff which may be taken up by the fibre, as
Knecht has found that wool is capable of extracting far larger
quantities from concentrated dye-baths. If a calculation be made
based on the amount of picric acid which is taken up by the fibre,
it is found that the maximum amounts of naphthol yellow S,
tartrazine, and crystal violet which may be combined with wool
closely approximate to molecular quantities.

Another conclusion which follows from the researches of the
same chemist, is that many cases of so-called substantive dyeing
are in reality adjective. In the case of wool, for example, a com-
pound has been isolated, called lanuguinic acid, and it has been
found that this acid is capable of entering into combination with
dyestuffs, producing compounds which, although amorphous, closely

6 INTRODUCTION.

resemble dyed wool in their properties. It is possible that in
dyeing wool the action of boiling water liberates this substance,
which then effects the combination with the dyestuffs. In this
hypothesis, the lanuguinic acid is supposed to be retained in the fibre
in a state of solid solution.

A theory of solid solution has been applied in a somewhat
different form by Witt to the substantive dyeing of wool, silk, and
cotton. A skein of silk dyed with magenta is according to the
chemical theory a combination of magenta and silk, and it requires
pretty strong soaping to remove the dye. But if the silk be treated
with alcohol, which is certainly capable of exerting only a solvent
effect, all the colouring-matter is quickly removed. If water is
added to the alcoholic solution, the dyestuff, however, returns to
the silk. This behaviour, unexplained by the chemical theory of
dyeing, may be cleared up by the " solid solution " theory. In
this especial instance of silk and magenta, we must suppose that
the essential constituent of the silk fibre, fibroin, has a greater
solvent action for magenta than water, and thus withdraws it
from its aqueous solution. Alcohol having a greater solvent
power than the fibroin, removes the dyestuff from the fibre.
Similar cases are frequent in purely chemical operations, and the
extraction of magenta from its aqueous solution by silk is exactly
similar to the removal of resorcin from an aqueous solution by
ether.

The different behaviour of various textile fibres in dyeing may
be explained by an assumption of different solvent power ; thus,
silk dyes more readily than other fibres because the fibroin has a
greater solvent power. Keratine again, the principle of the wool
fibre, possesses a greater solvent power than cellulose, which is
only capable of attracting and holding in solution a few dyestufi's,
such as the tetrazo-dyes of the benzidine series, and in certain
cases in this class the solvent power of the water in the dye-bath
has to be decreased by addition of salt.

The mechanical theory of dyeing is based on the assumption that
the molecules of colouring-matter leave the dye-bath and are
mechanically deposited between the molecules of the fibre.

Certain plant-fibres — for example jute, the bast-fibre of Cor-

INTRODUCTION. 7

chorus — have the property of fixing dyestuffs directly, this being
due to the presence o£ an incrustation of foreign matter, present on
the fibre.

Many amorphous substances, amongst which may be mentioned
precipitated sulphur, gelatinous silica, and Kieselguhr, have the
power of attracting basic dyestuffs.

The properties of the so-called oxycellulose are also of interest
from a tinctorial standpoint. On oxidation of vegetable fibre
(cellulose) with chlorine, chromic acid, or similar agents, it under-
goes a change, and becomes capable of fixing basic dyestufi's without
a mordant.

A consideration of the radicals capable of acting as chromophors
shows that only two of these, the nitro- and nitroso-groups, are
monatomic. If these groups are introduced alone into a hydrocar-
bon, the body produced possesses scarcely any colour. A coloured
body is formed if a salt-forming group be also introduced, the
latter probably forming a closed ring with the chromophor. The
case is similar when a valent chromophor is introduced into
several hydrocarbons, so that each valency is attached to a hydro-
carbon group not in linkage with any other. This is the case with
the ketones, while the diketones (quinones) and simple ketones
possessing a ring constitution (diphenylene ketone) are coloured
compounds.

Azobenzene forms an apparent exception to this rule (see
below).

The ketone group, especially when it occurs twice, as in the
quinones, is one of the most important chromophors. The oxygen
atom of the ketone group may be replaced by another diatomic
radical, such as sulphur ; or the ketone carbon atom may enter
into combination with two valencies of a diatomic nitrogen atom :
the resulting groups C=S and C=:N in general possess increased
chromophoric properties. As an example of this, it may be
remarked that the derivatives of simple ketones are colourless,
those of the thioketones, ketone-imides, and hydrazides being
coloured.

The ketone group C=0 appears only to act as a chromophor when
it occurs as a member of a closed ring of carbon atoms. A large

INTRODUCTION.

number of dyestuffs may be regarded as built up similarly to the
di-ketones (ortho- and para-quinones) ; and as the present view
of the constitution of the quinones is expressed by the following
formula, the formulae of a large number of dyestuffs have to be
modified accordingly.
O

O Quinone.

The indamines are derivatives of quinone-imide, and accordingly
a change from a tertiary to a secondary carbon atom must be
accepted in the constitutional formula of these bodies.

Indophenol.

NH Nil

Quinone- imide Indamine.

(unknown).

A similar constitution may be accepted for rosaniline and
rosolic acid.

C=(CeH,NH2)2 C=(C6H,OH)2

Eosaniline.

0
Eosolic acid.

INTRODUCTION.

In these cases the oxygen of the ketone group is replaced by a
diatomic methane rest.

A class of bodies closely resembling the paraquinones are the
orthoquinones, for example yS-naphthaquinone and plienan-
threnequinone are members of this class of compounds. From
these a new class of compounds may be obtained, and these bodies,
the azines, are in some respects analogous to the paraquinones.

If an orthodiamine interacts with an orthoquinone, the oxygen
atoms of the latter are eliminated, and tertiary nitrogen atoms
enter in their places, a new ring containing two nitrogen atoms
and four carbon atoms being formed. The similarity of this ring
to the paraquinone ring exists in the fact that in the former tertiary
nitrogen atoms take the place of the chromophoric C=0 groups of
the latter.

This analogy is especially marked if the constitutional formula of
authraquinone is compared with that of the simplest aromatic azine.
CO '' N

Anthraquiuone.

N
Phenazine.

There are also certain points of resemblance between the azines
and quinoliue and acridine : here only one carbon atom is re-
placed by nitrogen, and it is probably owing to this that the
chromogenic nature of these bodies is not so strongly marked as
that of the azines.

N N

C
II

ClI

lO INTRODUCTION.

Generally speaking, the introduction of the simplest chromo-
phors gives rise to yellow dyestuffs, and when stronger and more
complex groups are introduced the colour changes through red
to blue &c. For example, all quinoline and acridine dyestuifs
are yellow, while only the simplest azines have this colour and
become red and blue by introduction of salt-forming groups.

In some other dyestuffs the presence of the lactone ring
C=0 — O — is assumed, and here again the oxygen atom may
be replaced by a primary nitrogen atom (indigo dyestuffs) .

It will be noticed, on examining the constitution of the chromo-
gens already treated of, that most of them contain the chromo-
phor as member of a closed ring, differing from the other
members in valency and linkage.

For instance, compounds constituted on the quinone type
contain two secondary and four tertiary carbon atoms. In cases
where four secondary carbon atoms are present, as in rhodizonic
acid, C6(OH)204, the body is still coloured; but if all the six
carbon atoms of benzene become secondary, as in triquinoyl or
perquinone, CcOe, the colour disappears ■'^. The same occurs if all
the carbon atoms of quinone become tertiary, i.e. by reduction of
the quinone to hydroquinone.

An attempt to explain the colours of all carbon compounds
by the existence of such rings possesses great interest, but it cannot
be denied that the necessary conditions are absent in numerous
dyestuffs, for example, thioketones, ketone-imides, and hydrazides
are such bodies, i. e. tetramethyldiamidothiobenzophenone and
auramine,

(CH3)2 N-CeH,-C-C6H,-N(CH3)2,
II

(CH3)o-N— C6H-C-C6H,-N(CH3)2,
II
NH

in which the chromophors CS and CNH are not present as a ring
but as an open chain.

* The researches of Hantsch (Ber. xx.) make it improbable that the absence
of colour in triquinoyl and leuconic acid is due to hydration.

INTRODUCTION.

Tlie nitro-compoundsj whicli are almost the only class in which
a monatoniic group acts as chromophor, would also be difficult to
bring under the above ring classification. There is no doubt,
however, that in amido- and hydroxyl derivatives of nitro-bodies
there is a certain relationship between the nitro-group and the
hydroxyl or amido-group. It is not improbable that the nitro-
phenols possess a similar constitution to the nitrosophenols, which
are now generally regarded as quinoneoximes. The azo-dyc-
stuffs are a class of bodies the properties of which are not in
accordance with their constitution, and this is especially marked
in the first member of the series, azobenzene.

If a single hydrogen atom in a benzene ring is substituted, or if
two rings are joined together by a diatomic radical, the bodies
formed are colourless or only slightly coloured, while azobenzene
is an intensely coloured compound and a powerful chromogen.

This leads to the supposition that azobenzene does not act
according to the simple constitutional formula CeHsN^NCgH,
in certain cases, and other facts tend to speculation as to a
more complex formula.

Azobenzene and its derivative hydrazobenzene may be con-
verted into a derivative of diphenyl, benzidine ; and the ease with
which this reaction takes place seems to point to the existence of
an unstable linkage between the benzene rings. This would be
most readily explained by the assumption that a change in the
linkage (from double to single) between the carbon atoms in the
benzene chain takes place in a similar manner to the linkage in the
quinone formula.

The following formula would then express the constitution of

azobenzene : —

N N

13 INTRODUCTION.

Naturally such formulse are hypothetical, and only of interest in
attempting to regard all dyestuffs as variations of a common
system.

A characteristic of the radicals which act as chromophors is
that they are never perfectly neutral groups, or in other words
their introduction confers a certain tendency towards basic or acid
properties to the bodies which they enter.

By introduction of salt-forming groups these properties become
strengthened in one or other of these directions. According to
their nature, therefore, these chromophors may be classified as
basic or acid-forming. The quinone group, for example, possesses
strong acid-forming properties. A simple hydroxyl derivative
of a hydrocarbon possesses weak acid properties, while the hy-
droxyl derivatives of the quinones have these properties in a far
higher degree. The nitro-group acts similarly. Chromophors
which contain nitrogen without oxygen tend to form bases.

We have still to consider more closely the nature of the salt-
forming groups which have already been mentioned.

These groups may act totally difterently, and are divided into
two sharply defined classes.

Certain radicals, generally acid, such as the sulpho-group,
SO3H, and the carboxyl group, if introduced into a chromogen,
confer upon it acid properties, but without increasing the colour
appreciably, indeed in many cases the dyeing power is considerably
decreased.

Such bodies act as acid dyestuffs, and the group introduced
effects the combination with the fibre.

Azobenzene, for example, has no affinity for animal fibres, being
perfectly neutral, while its sulphonic and carbonic acids act as
weak dyestuffs. The influence of amido- and hydroxyl groups is
a totally different one.

By introduction of these radicals the chromogen acquires basic
or acid properties, and at the same time a considerable modifica-
tion in the colour of the body is produced. The colour generally
becomes more intense; in many cases colour is only produced
when these groups enter. Having regard to these facts the
groups (sulpho- and carboxyl) may be termed " salt-forming,'^

INTRODUCTION. 13

while for tlie latter Witt lias recently suggested the name
aiixochromic (Ber. xxi. p. 325).

The relationship existing between these groups and the chro-
mophors is not yet explained. In the case of the oxyquinones
it has already been pointed out that the chromophoric quiuone
group confers strong acid properties on the auxochromic hydro-
xyl group. The same is also observed in the phthale'ins and
rosolic-acid dyestufFs. These hydroxyl groups play at the same
time the part of salt-formers, and produce the necessary affinity
for the fibre. The auxochromic amido-groups exert a somewhat
different influence on the base-forming amido-groups. This
behaviour may easily be explained by studying the basic triphenyl-
methane dyestuffs, for instance rosaniline. llosaniline contains,
besides the chromophor =C=R=NH, two auxochromic amido-
groups.

It is certain that the imide group of this chromophor
combines with the acid in the formation of the red monoacid
rosaniline salts, and it is by its means that the combination with
the fibre is effected. The latter is deduced from the fact that
rosaniline dyes the colour of these salts, while the salts formed
by neutralising the two amido-groups are yellow.

The amidoazines show this characteristic in a somewhat more
striking manner. The azines contain the chromophor : —

and the simplest members of the scries are weak bases forming
salts which are mostly red or violet and only stable in presence of
an excess of acid.

The amidoazines, for example toluylcne red (diamidoazine), are
strong bases forming red monoacid salts, which, however, are stable.

Here also the acid radical is combined with the azine group,
and the amido-groups only form salts in presence of an excess of
acid, the change being accompanied by a characteristic change of
colour through blue to green.

14 INTRODUCTION.

In dyeing, toluylene red produces a red shade, and not a blue
or green, so that the azine group alone enters into combination
with the fibre.

It is easily seen that in these cases the auxochromic amido-
groups tend to strengthen the basic character of the chromophor,
but do not act as salt-formers. At the same time the colour
becomes more intense. According to a rule which has been laid
down by Witt, the stronger of two similar dyestuffs is always that
which possesses salt-forming properties in a higher degree.

From this it may be conceived that the simultaneous presence
of a basic auxochromic group and an acid-forming chromophor, or
vice versa, gives rise to a weak dyestuff. The nitranilines form a
case in point ; they are weak dyestuffs, while on the other hana
the nitrophenols have tinctorial properties much more fully
developed.

From the foregoing reasons actual dyestuffs are divided into
two principal classes — acid and basic.

Certain coloured bodies like indigo are neutral, and possess no
affinity for textile fibres. Their dyeing is effected by precipitating
on the fibre from a solution as in vat dyeing, or by converting
into a sulphonic acid, and thereby producing a capability to form
salts.

The salts of certain azosulphonic acids may be termed neutral
dyestuffs. They may be directly fixed on vegetable fibres.

Most basic and acid dyestuffs are fixed without aid by animal
fibres ; vegetable fibres, on the other hand, require the interven-
tion of a special mordant. Tannic acid is generally used along
with basic dyestuffs, as it forms insoluble salts with these com-
pounds.

Cotton possesses the power of attracting a certain amount of
tannic acid from solutions containing this body, and of retaining
it even after washing. Cotton prepared in this manner may be
dyed with most basic dyestuffs just as well as wool. In practice
the cotton treated with tannic acid is further submitted to the
action of tartar emetic or some other antimony compound. An
insoluble salt of tannic acid and antimony oxide is formed, and

INTRODUCTION. 15

this fixes basic dyestutfs with the greatest ease. The advantage
of the latter method is that the shades produced are faster to
soap. Some acid dyestuffs combine with metallic oxides, pro-
ducing insoluble lakes, different in colour to the original dyestuffs,
and varying considerably with the metallic oxide used. This
property is much used to effect the fixation of dyestuffs on the
fibre, especially on cotton. Anthraquinone derivatives are always
fixed in this manner, and numerous natural dyestuffs also.

This peculiar property of dyeing on metallic mordants has as
yet had no satisfactory explanation. If cotton mordanted with
alumina or oxide of iron is placed in an alizarin bath, the lake is
precipitated and enters into intimate combination w ith the fibre.

Many dyestuffs form insoluble lakes with metallic oxides, but
the property of combining with mordants on the fibre is peculiar
to a few. Insoluble lakes may be obtained from the eosines and
from all oxyanthraquinones, but the former class of bodies can-
not be fixed on mordants, and of the latter only derivatives of
alizarin possess this property.

It is necessary that the lake produced forms a certain combina-
tion with the fibre ; if not, it is only retained superficially, and is
removed mechanically during the dyeing process. It has been
found that this capability of dyeing on mordants stands in close
relationship to the constitution of the colouring-matter, and more
especially to the relative positions of the substituting groups
(compare quinone dyestuffs).

The commercial value of a colouring-matter is best determined
by dye-trial; in fact this is the only trustworthy method, and the
numerous processes which have been proposed to determine
dyestuffs volumetrically are untrustworthy, as they are readily
influenced by the nature of the impurities present.

Exceptions may be made in dealing with a few dyestuffs which
come into commerce in a pure state.

For instance, alizarin is tested by a dye-trial, and then examined
after washing carefully for the amount of solid matter and ash
which it contains.

The testing of colouring-matters by means of dye-trials is simply

16 INTRODUCTION.

colorimetric comparison of a dyestuff with a standard of known
quality. If equal quantities of two samples of a dye are dyed
upon equal weights of wool or silk, a diflference of two to five per
cent, may be distinguished from the difference in shade observed
in the two patterns.

By a second dyeing it is easy to determine the difference between
the quantities of the two dyestuffs required to produce the same
shade, and a simple calculation then gives the value of the product
tested, compared with the standard. At the same time an idea is
obtained of the relative purity of the shade of the dyestuffs and
of the nature of the impurities which may be present.

In printing, both basic dyestuffs and acid ones capable of forming
lakes with metallic oxides are employed.

The principle of the fixation of basic dyestuffs in printing
depends on the insolubility of the tannin compounds.

The tannates of all colour-bases are insoluble in water, but
mostly dissolve in dilute acetic acid. The dyestuff is printed
along with tannin and dilute acetic acid. The acetic-acid solution
of the tannin lake penetrates the fibre, and subsequent steaming
removes acetic acid, leaving an insoluble lake on the fibre. The
shades may be made faster to soap by passing through tartar
emetic.

Acid dyestuffs, like alizarin &c., are printed in the free state
along with the metallic mordants (aluminium, iron, or chromium
acetate) ; on steaming, acetic acid is driven off and the metallic
oxide combines with the colour-acid to a firmly adhering lake.

Only a few natural dyestuffs (indigo, alizarin, and purpurin)
have been prepared synthetically, but the number of artificial
dyestuffs is very large. Some of these, especially the phthaleins
and rosolic acid, seem to approach the natural dyestuffs in con-
stitution, but the greater number belong to special classes, which
are without analogue in either the animal or the vegetable kingdom.

Natural dyestuffs, with few exceptions (indigo, berberine),
contain only carbon, hydrogen, and oxygen ; while many classes
of artificial colouring-matters contain nitrogenous groups, often
of a decided basic nature. Some others again contain chlorine.

INTRODUCTION. 17

bromine, iodine, or sulphur. The raw materials for the preparation
of these bodies are, at the present time, almost exclusively jjroducts
of dry distillation, and the most important of these is coal-tar,
obtained as a bye-product in the manufacture of illuminating-gas.
The discovery and first preparation of artificial dyestuffs is there-
fore closely associated with the earliest studies on products of dry
distillation ; and the development of the gas industry has, hand in
hand with a series of scientific researches appertaining there-
to, brought the important colour-manufacturing industry into
existence.

The honour of preparing the first colouring-matters from
products of dry distillation belongs to von Reichenbach (pittacal
from wood-tar, 1832), and to Runge (rosolic acid from coal-tar,
1831) [1].

For a long time, however, the discoveries of these chemists
remained in obscurity, and it was only after the knowledge of
products of dry distillation had been considerably advanced by
later researches, that the production of coloured derivatives again
attracted the interest of chemists.

Hofmaun, Zinin, and Fritsche were the first to show the
relationship between benzene, aniline, phenol, &c. ; and the first
explanation of the constitution of these products formed the
foundation of the colour-industry.

The first dyestuff prepared and applied on an industrial scale
was '^ mauve," introduced by Perkiii in 1856. About the same
period the formation of rosaniline was noticed by Nathanson,
who obtained it by heating aniline with ethylene chloride [2] .

Two years later Hofmann [3] announced the discovery of a red
product, obtained by the action of carbon tetrachloride on aniline.
Hofmann and Nathanson, if their experiments were made with
pure aniline, must have already had pararosaniline in their
hands.

The next ten years were almost entirely devoted to the scientific
study and technical development of rosaniline and its derivatives.

The first patent was taken out by Reiiard freres and Franc, of
Lyons, on April 8th, 1859 [4], for the preparation of a red dyestuff,

18 INTRODUCTION.

according to a process discovered by Verguin, which consisted in
the action of stannic chloride on aniline.

Numerous patents followed in England and France, depending
on the action of other oxidising agents than stannic chloride. In
some of these patents, however, it is not clear whether rosaniline
or some other dyestuff such as mauve is really produced. E-enard
frcres introduced their products, still very impure, under the
name "fuchsine."

The process of Gerber-Keller with nitrate of mercury is the
only one of any value (October, 1859) [5].

In the following year, 1860, the application of arsenic acid as
oxidising agent was patented by Medlock and by Nicholson almost
simultaneously in England [6]. A few months later the same
process was made the subject of a French patent by Girard and
De Laire [7].

In 1861 Laurent and Castelhaz [8] patented the action of nitro-
benzene on iron and hydrochloric acid, and this is evidently the
first opening of the nitrobenzene process. In the same year the
synthesis of rosolic acid was effected by Kolbe and Schmitt [9] .

The formation of aniline blue was also first observed in 1861
by Girard and De Laire ; and in the following year the process
was further developed by Nicholson [10], by Monnet and Dury
[11], who used acetic acid in the manufacture, and by Wanklyn
[12], who applied benzoic acid.

In 1862 the composition of rosaniline, and its formation
from aniline and toluidine, was further explained by A. W.
Hofmann [13].

Aldehyde green was also discovered in 1862 [14].
In 1863 the same chemist prepared ethyl- and. methyl-deriva-
tives of rosaniline, and showed aniline blue to be triphenyl-
rosaniline [13].

Aniline black was first prepared in 1 863 by Lightfoot [1 5] .
The first azo-dyestuffs were introduced between 1864 and 1866.
Amidoazobenzene [16] appeared first, and was quickly followed by
phenylene brown [1 7] .

Caro and Wanklyn [18] demonstrated the relationship between

INTRODUCTION. 19

rosaniline and rosolic acid in 18GG ; and in the same year Keisser
took the first patent for iodine green [19] .

Diphenylamine bine was prepared by Girard and De Laire in
1867 [20].

In the same year methyl violet, which had already been noticed
by Lauth in 1861, was manufactured on a large scale by Poirrier
and Chapat.

The composition of iodine green was determined by Hofmann and
Girard in 1869 [21] ; and Rosenstiehl demonstrated the existence
of several rosanilines [22] .

The synthesis of alizarin was carried out by Graebe and Lieber-
mann [23] in the same year, this being of very great importance,
as the first synthesis capable of industrial application for production
of a dyestuff occurring in nature.

In 1872 Hofmann and Geyger [24] examined induline and saffra-
niue, the latter a dyestuff which had appeared in commerce a
few years previously.

In 1873 Hofmann published his researches on methyl violet
and methyl green [25] .

In 1874 the phthalei'ns (eosine), discovered by Bayer and Caro,
were introduced into commerce.

In 1876 pararosaniline Avas discovered by E. and O. Fischer, and
the relation of this body to triphenylmethane demonstrated [26] .

In 1877 Prud'homme discovered alizarin blue; its industrial
production was effected by Brunck in the following year.

In the same year Caro [27] produced methylene blue, basing
his process on the sulphuretted hydrogen reaction observed by
Lauth in 1876 [28]. Almost simultaneously malachite green
was discovered by E, and O. Fischer [29] and by Doebner [30] ;
and O. N. Witt and Roussin introduced the synthesis of azo-dyes
on a manufacturing scale, which proved afterwards to be of such
great importance.

In 1880 Bayer took out the first patent for the production of
artificial indigo [31].

In 1881 this was followed by indopheuol [32] and the gallo-
cyanine of Witt and Koechlin.

20 INTRODUCTION.

In 1883-84 Caro and Kern [33] effected the synthesis of tri-
phenylmethane dyestufFs by means of carbon oxychloride, and this
■was applied to the production of auramine and Victoria blue.

The constitution of numerous dyestuffs has been determined by
purely scientific researches, and these have been of great service
in discovering new synthetical methods, many of which are applied
on a large scale.

In 1886 an important development took place in the azo colour-
industry. This was based on an observation made by Griess (pat.
1884), that certain azo-dyestu flFs derived from benzidine were
capable of dyeing vegetable fibres without mordant. As members
of this class of dyestuffs, which are very numerous, may be
mentioned chrysamine, congo red, benzo-purpurine, &c.

In 1888 Witt explained the constitution of the saffranines by
his classic researches on the azines; and not long afterwards,
Fischer and Hepp proved that the indulines were also derivatives
of azines.

The rhodamines, a class of dyestuffs allied to the phthaleins,
were introduced in 1888.

The present requirements of the colour-industry as raw materials
are benzene and its homologues (toluene and xylene), naphtha-
lene, and anthracene, obtained from coal-tar. The coal-tar of
the gas-works is first worked up in tar-distilleries, the above bodies
being obtained in a more or less impure state. The further purifi-
cation is carried on in some colour- works ; but this generally
takes place in intermediate manufactories where the crude products
are purified and worked up into a higher stage, benzene and its
homologues being made into aniline, toluidine, and xylidine, and
naphthalene into naphthylamine. The crude benzol is first sub-
mitted to a careful fractional distillation, and benzene, toluene,
and xylene are separated in as pure a state as possible. The
hydrocarbons boiling at a higher temperature find their principal
application for solvent purposes, hence they are principally met
with under the designation " solvent naphtha/^ One purpose for
which it serves is the purification of anthracene. Benzene,

INTRODUCTION. 21

toluene, and xylene are converted into aniline, toluidine, and
xylidine by nitration and subsequent reduction.

These bases are at present prepared by aniline-works in a state
of great purity ; for instance the aniline employed in the manu-
facture of blue ("blue oil") is required to be chemically pure.

The "red oil" used in the manufacture of rosaniline is a
mixture containing aniline, ortho- and para-toluidine in varying
proportions.

A classification of the organic clyestuifs from a chemical stand-
point is in many respects a subject of great difficulty. Most
text-books have adopted a division in which the dyestuffs are
classified according to the hydrocarbon from which they are
derived ; this, however, is far from natural, as by its means some
groups which are chemically well characterized, such as the azo-
dyes, are divided ; and, on the other hand, dyestuffs of totally
different constitution are placed together.

In the following classification an attempt is made to group
the colouring-matters according to their chemical constitution,
especial regard being paid to their colour-giving groups. In many
cases this is rendered difficult, however, by the somewhat scanty
knowledge of the relations existing between constitution and dye-
stufi" character.

The final class, " Dyestufis of unknown constitution," is still
a very numerous one.

This group comprises most natural dyestuffs : the constitution
of some of these (alizarin and indigo) is known, and admits of
systematic classification with just as much justice as the purely
artificial dyestufi's; and it would be reasonable to treat of the
whole in a single chapter of natural dyestuffs.

It must not be conceived that the constitution of all the colouring-
matters here classified is completely explained, in many cases
it is deduced from analogy in formation to that of bodies of
known constitution; but as to the constitution of dyestufis which
have not been prepared synthetically, we are altogether without
knowledge.

22 INTRODUCTION.

The organic colouring-matters may be grouped as follows
I. Nitro-Compounds.
II. Azo-Compounds.

III. Oxyquinones and Quinoneoximes.

IV. Ketone-imides and Hydrazides.
V. Triphcnylmethane Derivatives.

VI. Quinone-imide Dyestuffs.

VII. Azine Dyestuffs.
VIII. Aniline Black.

IX. Indulines and Nigrosines.
X. Quinoline and Acridine Dyestuffs.

XI. Indigo Dyestuffs.
XII. Euxanthic Acid and Galloflavine.
XIII. Canarine.
XIV. Murexide.

XV. Dyestuffs of unknown constitution.

CHEMISTRY

OF THE

ORGANIC DYESTUFFS.

CHAPTER I.

NITRO-COMPOUNDS.

The nitro-derivatives of amines and phenols are dyestufFs, of a
more or less pronounced character. The phenol derivatives have
the greater tinctorial power, as the nitro-group is a chromophor
which confers acid properties, and therefore possesses the power
of decreasing the basic properties o£ the amido-group. Indeed,
in the case of certain bodies of only feebly basic properties, the
introduction of several nitro-groups may produce an acid dyestufl",
for example, diphenylamine is a body of this class.

Acid nitro-compounds are especially strongly coloured in the
form of salts ; paranitrophenol, for example, is a colourless body,
yielding yellow salts. On the other hand, basic nitro-compounds
form colourless salts with acids.

The compounds produced when the acid properties of the
hydroxy 1 group are removed by introduction of an alcohol radical
are colourless, for instance, nitroanisol behaves like a nitro-
derivative of a hydrocarbon.

Those nitrophenols which contain the nitro-group and the
hydroxyl group in the ortho position to each other, are as a rule
the most strongly coloured.

The close relationship existing between the nitrophenols and

24 CHEMISTRY OF ORGANIC DYESTUFFS.

the nitrosophenols, and the assumption generally accepted, that
the latter are quinoneoximes, render it probable that a similar
structure may be ascribed to the nitrophenols, and that in the
latter there is a certain connection between the nitro and hydroxyl
groups.

The number of coloured nitro-compounds is very large, and in
the present place it is impossible to consider more than those which
possess technical interest. They are all acid dyestuffs ; since the
introduction of the azo-dyestuffs their application has become
considerably less.

Trinifrophenol (Picric Acid) [1, 2, 3].

Picric acid is formed by the action of nitric acid on phenol,
and on many other organic bodies (indigo, xanthorrhtca resin,
aloes, &c.). On a large scale it is obtained by the action of con-
centrated nitric acid on phenol-sulphonic acid [2].

In a pure state picric acid forms light yello^y leaflets, M.P.
122°' 5 C. It dissolves somewhat sparingly in water, more easily
in alcohol.

It forms well crystallized salts with metallic oxides ; the
potassium salt, C6H2(N02)OK, is difficultly soluble. Picric acid
dyes wool and silk from an acid bath, a fine greenish shade of
yellow being produced. Although this shade is not fast, it finds
considerable application in silk-dyeing, and serves principally for
production of compound colours, especially for modifying green
and red dyestuffs. '

Dinitrocresol.

P TT CH3OH

The sodium salt of a dinitrocresol formerly came into commerce
under the name '' Victoria Yellow " or Saffron substitute [5] .

It was probably obtained by treating crude creosol with nitric
acid, partly also by diazotising crude . tbluidine and boiling the
resulting compounds with nitric acid. It consists chiefly of a
mixture of dinitroparacresol (CH3 : OH : NOg : N02 = l .4.3.5),
M.P. 83°-5, and dinitro-orthocresol (1 . 2 . s'! 5), M.P. 85°-8 [4].
It is now, however, almost out of the market.

NITRO-COMPOUNDS, 25

Dinitronajjhtliol (Martius Yellow).

CioH5(NOo)oOH.

Dinitro-a-naphtliol was formerly obtained by boiling a-diazo-
naphthalene [6] with dilute nitric acid ; at the present time it
is manufactured by the action of nitric acid on a-naphthol sul-
phouic acid (mono- or di-sulphonic acid) [7].

Pure dinitronaphthol forms needles, which are sparingly soluble
in water and difficultly soluble in alcohol^ ether, or benzene. It
melts at 138°, and forms salts which are moderately soluble in
water.

The commercial product is generally the sodium salt, though the
lime salt is occasionally met with. It dyes wool and silk in an
acid bath, a fine golden-yellow shade being obtained. The principal
drawback in the use of this dyestuff is that it is volatile at a com-
paratively low temperature, and is therefore liable to mark off.

Another application of dinitronaphthol is for colouring con-
fectionery, as it does not possess the bitter taste peculiar to most
nitro-compounds.

Binitronaphthol Suljilionic Acid (Naphthol Yellow S.)

CioH4(NOo)o6hhS03.

By the action of nitric acid on a-naphthol mono- and di-sul-
phonic acids (obtained by direct sulphonation), the sulpho-groups
are replaced by nitro-groups, while on nitration of a-naphthol
trisulphonic acid, one sulpho-group remains intact [8], the other
two being replaced by nitro-groups. The compound formed is a
monosulphonic acid of dinitronaphthol. This acid forms long
yellow needles, which are easily soluble in water [9].

The commercial product consists of the potassium salt, which is
sparingly soluble. On wool and silk it dyes the same shades as
INIartius yellow, but is to be preferred as yielding much faster d\ es.

It may be distinguished from Martius yellow by treating its
solution with acids ; Martius yellow is immediately precipi-
tated, while naphthol yellow S gives no reaction.

26 CHEMISTRY OF ORGANIC DYESTUFFS.

Brilliant Yellow.

This dyestiiff is prepared by the nitration of the a-naphthol
disulphonic acid of the Schollkopf Co. It is an isomer of naphthol
yellow S, but little is known of its dyeing properties.

Tetranitronaphthol [10].

CioH3(N02)/)H.

Tetranitro-a-naphthol is obtained from tetranitrobromnaph-
thalene by treating with an alkali. It forms yellow needles which
melt at 180°. It gives fine orange shades on wool and silk, but
it is not fast to light, and has only obtained slight appreciation
under the designation *' Sun gold.^^

Tetranitrodij)henol.

(NO,U „„//(N0,),

OH/ ' ^ " "NOH

This colouring-matter formerly came into commerce in form
of its ammonium salt as '^Palatine orange/^ and was used in
paper-dyeing. It is formed by treating benzidine with nitrous
acidj and boiling the resulting tetrazodiphenyl with nitric acid.

Ilexanitrodiphenylamine (Aukantia) [11].

(N02)3C6H2NHC6H2(N02)3.

Hexauitrodiphenylamine is produced by energetic action of
nitric acid on diphenylamine. It forms yellow prisms, M.P. 238°,
and behaves like an acid, forming stable crystalline salts with the
alkalies. It dyes an orange shade on silk and wool, but since the
introduction of the azo-dyes is scarcely ever used.

Salicyl Yellow (Nitrobromsalicylic Acid) [13].

The nitro-compounds which are formed by treating monobrom-
salicylic acid with nitric acid have been tried experimentally in
dyeing. They are very fugitive to light, and this, together with
their high price, renders them unsuitable for technical application.

NITRO-COMPOUNDS. 27

Mononitrobromsalicylic acid dyes a very pure yellow on wool and
silk from au acid bath, the dinitro-compound yields a more orange
shade.

Isopurpuric Acid.
CgHsN.Oo.

The potassium salt of this acid, which is also known as picro-
cyaminic acid, is obtained by treating picric acid with solution of
potassium cyanide. The ammonium salt obtained from the
potassium salt by double decomposition with ammonium chloride
was formerly used in dyeing under the name " Grenat soluble/^
It produces reddish-brown shades on wool and silk, but has now
entirely disappeared.

Another colouring-matter which formerly occurred in commerce
is picramic acid, C6H2(N02)2NH20H, obtained from picric acid
by partial reduction.

28 CHEMISTRY OF ORGANIC DYESTUFFS.

CHAPTER 11.

AZO-COMPOUNDS.

The Azo-dyestufPs form a well-characterized group o£ compounds
containing the azo-chain — N=N — as chromophor.

This divalent group is always linked with two benzene rings or
other aromatic hydrocarbon^ and thus differs from the diazo-group,
which is similarly constituted in other respects. The introduction
of the azo-group into hydrocarbons or bodies acting similarly
(anisol, phenetol) gives rise to the formation of coloured com-
pounds, which, however, are not dyestuffs. The affinity for fibres
is only acquired when groups are introduced which confer acid or
basic properties to the azo-compounds.

Azobenzene, though intensely coloured, is not a dyestuff.
Azobenzene-sulphonic acid possesses tinctorial properties, although
only to a slight extent ; but if auxochromic groups, such as the
amido or hydroxyl groups, are present, the dyeing power is con-
siderably increased, and at the same time the shade is considerably
modified. It is probable that in this class of compounds there
exists a certain linkage between the auxochromic and the chromo-
genic groups, this linkage being easily dissolved under certain
circumstances.

Liebermann deduced the following formula for /3-naphthol-azo-
benzene [1],

I /CioHg,

from the fact that this body does not act as a phenol. In a similar
manner Zincke ascribes one of the following formulae to the com-
pound produced by the interaction of diazobenzene and yS-naph-
thylamine [2] : —

AZO-COMPOUNDS. 29

pCoHe or CJl5-N<j5{{>CioH6.
H

It cannot be denied that many reactions of oxy- and amidoazo-
compounds, especially those of the ortho series, are easily explained
on the assumption that these formulae are correct; but, on the
other hand, amidoazo-compounds are capable of reacting as true
amines.

The above formulae show a certain analogy to the quinones,
especially marked, if written slightly differently,

C6H5-NH-N=CioHe = 0 and C6H5-NH-N = CioH6 = NH.

An important support for this theory is the circumstance that
the bodies formed by the action of aromatic hydrazines on
quinones are identical with those obtained from phenols and
diazo-compounds. Phenylhydrazine, for example, reacts with
a-naphthoquinone, producing the same compound which is formed
by combination of a-naphthol with diazobenzene [3j. The first
method of formation renders the formula

C6H5-NH-N=CioH6=0

probable, while the latter affords just as good reason for the
formula

CeH5-N = N-CioHe-OH.

The compounds from hydrazines and ketones or quinones
(hydrazides) are so closely related to the azo-series, that one is
almost compelled to place them under the same classification.

The property of forming combinations with sodium bisulphite is
common alike to azo-dyes, ketones, and quinones [4]. A differ-
ence in the constitution of ortho- and para-derivatives cannot well
be accepted, as the same reactions may be obtained with each,
though with varying degrees of ease.

As has already been stated, the azo-compounds react like amido-
or hydroxyl compounds in certain cases; for example, aii amido-
azo-compounds yield diazo-compounds. It is possible that two
forms exist in such cases, and that these react in one way or
another according to circumstances.

30 CHEMISTRY OP ORGANIC DYESTUFFS.

The older constitutional formulae have been used in the following
pages, this being the general method, and as there is just as much
evidence in favour of the old formulaj as there is for the new.
The simplest azo-compounds, like dyestuffs of simple constitution,
have in general a yellow colour. By increasing the number of
auxochromic groups, or by building-up of carbon atoms in the
molecule, the shade becomes deeper. In many cases it goes
through red to violet, in others it becomes brown. Blue dyestuffs
of this class have only been obtained by introduction of several
azo-groups in the molecule (dis- or tetrazo-dycstuffs).

Azo-dyestuffs of a green colour have not yet been obtained,
although many form green compounds with acids.

The so-called ^'azo-green,^^ although containing an azo-group,
owes its colour to the rest of tripheriylmethanc present.

Dyestuffs which contain benzene and no higher hydrocarbon are
mostly yellow, orange-yellow, or brown. By the introduction of a
naphthalene group, red colouring-matters are formed, and blue and
violet dyestuffs are obtained if the naphthalene ring occurs several
times.

The introduction of a radical of totally indifferent properties (as
the methoxyl group, — O CH3) may produce a great alteration in
the colour of the compound operated upon.

The relative positions of the chromophor groups have also a
decided influence in this direction. The compound

(H 803)2^ /(H 803)2

^g;C,oH,-N2-CeH,-N2C,oH,(^|^

is blue if the azo-groups are in the para-position in the benzene
ring, and red if in the meta-position.

The general rule that the depth of colour of a compound
increases with the number of atoms constituting the molecule, does
not apply in all cases ; for example, the above dyestuff is redder, if
the connecting benzene ring is replaced by a higher hydrocarbon.

Nearly all azo-dyestuffs give characteristic colour-reactions on
dissolving in strong sulphuric acid^ and it is probable that in such
cases the basic properties of the azo-group become apparent by the
action of the strong acid. It is worthy of notice that most sub-
stituted azo-dyes give the same reaction with sulphuric acid as the

AZO-COMPOUXDS. 31

azo-liycli*ocarl)on from which tliey are derived. Azobcnzene dis-
solves in sulphuric acid with a yellowish-brown colour; and the same
colour is obtained with its oxy- and amido-derivatives, although
the latter are coloured red by dilute acid, a-azo-naphthalene, and
its oxy- and amido-derivatives, give a blue coloration with concen-
trated sulphuric acid. In mixed azo-compounds the presence of a
sulpho-group may produce interesting changes according to its
position, ^-naphthol-azobeuzene, for example,

CeH^-No-CioHeOH,

dissolves in sulphuric acid with a red-violet colour, probably the
same which belongs to the mother substance,

CeHg — No — CtoH;.

The same colour is obtained if a sulpho-group occurs in the benzene
ring ; while, on the other hand, if this group is in the naphthol, the
compound dissolves with a yellow colour, the same as azobcnzene.

These phenomena may be explained on the assumption that the
sulpho-group exerts a salt-formitig action with one nitrogen atom
of the azo-chain ; and that in one case with the above compound,
the nitrogen atom attached to the benzene ring is influenced, in
the other that combined with the naphthalene.

These colour-reactions become more complicated if several azo-
groups are present in the molecule. '

Substituted azo-compounds are generally prepared by the action
of diazo-compounds on phenols and amines. With the latter
bodies the intermediate formation of diazoamido compounds is
often observed.

Experience has proved that the azo-group enters in the para-
position to the amido- or hydroxyl-group if this is free; if this
point is already substituted, the linkage takes place in the ortho-
position. Condensations in the meta-position have till now not
been observed.

Some azo-compounds may be converted into easily oxidisable
hydrazo-compounds by cautious reduction, while all are decom-
posed by the action of energetic reducing agents. In this case the
linkage between the nitrogen atoms is dissolved, each atom being
converted into an amido-group by addition of hydrogen. Azo-
bcnzene yields on reduction two molecules of aniline ; auiidoazo-

32 CHEMISTRY OF ORGANIC DYESTUFFS.

benzene gives one molecule of aniline and one molecule of para-
phenylenediamine,

CeH5N = N-C6H,NH2 + 4H = CeHgNHa-fH^N-CeH^-NHg.

This splitting up forms in many cases a means for recognition
of azo-corapounds and for determining their constitution. By far
the greater number of azo-dyestuffs used technically are sulphonic
acids, while the number of basic azo-dyes is limited. Amidoazo-
compounds of weak basic properties are not easily fixed in dyeing ;
they yield, however, useful basic dyestuffs if a second amido-group is
introduced into the ring, which already contains the auxochrome
group. Probably this second group does not act as an auxochrome ;
it has no connection with the azo-chain, and its function is appa-
rently to supply the necessary attraction for the fibre. If both
amido-groups are in different rings, the resulting compound acts
as a simple amidoazo-compound.

Chrysoi'dine,

for example, is a strong basic dyestufF, while in an isomer parazo-
aniline,

NH^CsH.-Ns-CsH.NHs,

this property is absent. Probably in the latter case both amido-
groups are influenced to a certain extent by the azo-chain, while
with chrysoi'dine this is only the case with one group.

The amido-groups acting as auxochromic groups are therefore
probably connected with the azo-group, and when combined with
acids to form salts show a striking alteration in colour, while the
amido-groups, which play merely a basic part, do not undergo
this change.

Chrysoi'dine, a case in point, forms stable salts with one molecule
of acid, and their colour is little different to that of the base, while
with an excess of acid a red di-acid salt is formed, which loses the
second molecule of acid on treatment with water. On the other
hand, amidoazobenzeue forms red salts which are decomposed by
water.

Parazoaniline, which in all probability contains two auxochromic
amido-groups, shows different colours according as one or both of
these groups are saturated. With acids it gives at first a green
colour ; in presence of excess, however, a red colour.

AZO-COMPOUNDS. 33

Certain facts render it donbtful whether the auxochromic amido-
groiips enter into combination with tlie acid radical in the forma-
tion of salts, and it is possible that the azo-group enters into
combination. Amidoazobenzene, a weak base, retains its basic
properties after acetylation, and forms red salts as before ; while
the simple amines such as aniline, which possess much stronger
basic properties, yield on acetylation almost completely indifferent
compounds. At any rate this fact strongly supports the assumption
that there is a certain linkage between the azo- and amido-groups.

The sulphonic acids of the amidoazo-compounds are interesting
in this respect. Apparently they arc incapable of existing in the
free state, at least from their colour it appears that the formation
of a salt takes place between the sulpho-group and the basic
group.

Amidoazobenzene in the free state is yellow, while its sul-
phonic acids have the red colour of the amidoazobenzene salts.
If, however, the sulpho-group is saturated by an alkali, the salt
produced has again the colour of free amidoazobenzene.

These amido-sulphonic acids beiiave like acid dyestuffs, but in
dyeing the fibre always takes the colour of their alkali salts or of
the free amidoazo-base.

The conclusions naturally drawn from this are that the sulpho-
group effects the combination with the fibre, and that the acid
properties of the former are saturated by the latter.

This property is still more striking with the sulphonic acid of
phenyl amidoazobenzene (Tropaolin 00) ; this body exhibits a
colour-change from orange to violet.

The azo-compounds, though long known, have attained most of
their importance in the last ten years, especially the scarlet-red
shades, which have almost entirely replaced cochineal. The first
azo-dyestuff used largely was triamidoazobenzene (phenylene
brown) discovered by Caro and Griess in 1867.

For ten years after this no particular progress was made in this
field, and the first synthetical production of azo-compounds
appears with the discovery of chrysoi'dine by Witt and Caro.

ChrysoYdine was rapidly followed by the introduction of the
acid dyestuffs, discovered, almost simultaneously by Witt and
Roussin, and which, since the introduction of naphthols, have
attained great importance.

The manufacture of azo-dyes is in general very simple. If a

34 CHEMISTRY OF ORGANIC DYESTUFFS.

diazo-compound has to be combined with a phenol^ the former is
prepared by dissolving the amine or its sulphonic acid in water, or
suspending them in as finely divided a state as possible, and adding
to the liquid the calculated quantities of hydrochloric acid and
sodium nitrite.

After diazotisation is completed the liquid is allowed to run
into an alkaline solution of the phenol or its sulphonic acid, care
being taken that the mixture remains alkaline. After some time
the dyestuff is salted out, and is generally filtered through a
filter-press. The combination of diazo-compounds with amines
is somewhat more complicated. Some of these, for instance
metaphenylenediamine, combine with diazo-compounds in neutral
aqueous solutions ; while others, like diphenylamine, are dissolved
in alcohol, and a concentrated solution of the diazo-compound
gradually added. In the manufacture of amidoazobenzene and
all compounds in which an intermediate formation of a diazo-
amido-compound takes place, a large excess of the amine has to be
employed, to hold the diazoamido-corapound formed in solution.

Sulphonic acids are generally obtained by combination of diazo-
sulphonic acids with phenols or diazo-bases with phenolsulphonic
acids, in a few cases also by heating the azo-compound with
fuming sulphuric acid.

The principal application of azo-dyestuffs is in wool-dyeing,
and all acid azo-dyes may be directly dyed on animal fibres from
an acid bath.

On cotton they are generally incapable of complete fixation, as
most of them form no real colour-lakes. Exceptions to this rule
are certain tetrazo-eompounds which dye cotton directly in the
form of alkali salts of their sulphonic acids.

Basic azo-dyes (chryso'idine, Bismark broAvn) are dyed like all
colour-bases on vegetable fibres prepared with tannic acid. Their
principal application is in cotton-dyeing.

A uniform method of nomenclature for all azo-compounds is
much to be desired, but the strict application of such a principle,
further than formation into groups, would lead to the necessity for
very long, and often unwieldy names, without insuring certainty
in regard to position.

For this reason such a method has been avoided, and the bodies
are in general described under the names given them by their
discoverers.

AMIDOAZO-COMPOUNDS. 35

I. AMIDOAZO-COMPOUNDS.

Amidoazohenzene [5, 6].

(1) (i)

C6H5-N=N-CJl4NH3.

Amidoazobenzene is formed by the molecular transformation
which diazoamidobenzene underj^^ocs when brought in contact
with aniline hydrochloride, best in aniline solution. It is there-
fore the final product of the reaction which occurs when a salt of
diazobenzene is treated with an excess of aniline, at a medium
temperature.

Its manufacture on a large scale depends on this principle :
Aniline is treated with such quantities of hydrochloric acid and
sodium nitrite, that about a third is converted into diazoamido-
benzene, and that the latter remains dissolved in the excess of
aniline. Further, the amount of hydrochloric acid is so calculated,
that after decomposition of the nitrite some aniline hydrochloride
remains in the mixture. The conversion of the diazoamido-
benzene is aided by warming gently, and, when complete, the
excess of aniline is saturated with dilute hydrochloric acid, and
filtered from the sparingly soluble amidoazobenzene hydro-
chloride.

Free amidoazobenzene forms yellow needles melting at 127°'5,
which may partly be sublimed without decomposition.

Its salts with acids are red and very unstable. They crystallise
well, and possess a bluish reflex. They are decomposed by water,
and are difficultly soluble in dilute acids, a red solution being
produced. "With concentrated sulphuric acid, amidoazobenzene
gives a yellowish-brown solution. It is easily split up on reduc-
tion, aniline and paraphenylenediamine being formed.

By cautious treatment with zinc powder in alkaline solution it
is converted into amidohydrazobenzeue, a colourless compound
which oxidises rapidly on exposure to the air.

Amidoazobenzene itself is useless as a dyestufP, but is important
as a starting-point for the manufacture of various dyestufis.

36 CHEMISTRY OF ORGANIC DYESTUFFS.

An isomer of amidoazobenzene^ which contains the amido- and
azo-groups in the ortho position, has recently been obtained by
Janovsky [7].

Amidoazolenzenemonosulplionic Acid [8, 9].

(1) (4) (1) (4)

HS03CcH4-N = N-C6H,NH2.

This acid is obtained with the disulphonic acid by treating
amidoazobenzene with faming sulphuric acid. It is formed in
small quantities by the action of paradiazobenzenesulphonic
acid on aniline hydrochloride. It may also be obtained by
cautious reduction of nitroazobenzenesulphonic acid.

As obtained by decomposition of its salts with hydrochloric
acid, it forms a gelatinous flesh-coloured precipitate, which after
some time changes to needles. Its salts throughout are sparingly
soluble in cold water, but dissolve easily in hot water. The
sodium salt forms golden-yellow leaflets.

AmidoazohenzenedisulpJwnic Acid [8, 9].

(I) (4) (1) (4)

HSO3 . C6H4N=N-C6H3NH3S03H.

This acid is produced by the energetic action of fuming sulphuric
acid on amidoazobenzene. It forms shimmering violet crystals
resembling chromic chloride, which on drying disintegrate.

The acid is easily soluble in water, but separates on addition of
a mineral acid. Its salts are yellow, very easily soluble, and
difficult to crystallise.

The sulpho-groups are present in both rings, and on reduction
the body yields sulphanilic and paraphenylenediaminesulphonic
acids.

Both these sulphonic acids of amidoazobenzene, and especially
the disulphonic acid, are valuable yellow dyestufi's, and the sodium
salt of the latter comes into commerce as Acid Yellow or Fast
Yellow. A further application of these acids is in the preparation
of tetrazo-dyestufi's, for example Biebrich- and Crocem-scarlets.

AMIDOAZO-COMPOUNDS. 37

Acetyl amidoazohenzene [71],

CeH,-N = N-CeH,N^j^Q,

forms yellow leaflets melting at 141°. It dissolves in liydro-
chloric aeid with a red eolour, and is only saponified on boiling.

iJimethylamidoazohenzene [10].

(1) (4)

C6H5-N=N-C«H,N™^

Limethylamidoazohenzenesidjjlionic Acid [11].

(1) (4) (1) (4)

HS03-C6H4-N = N-C6H4-N(CH3)3.

Dimethylamidoazobenzene is obtained by action of dimethyl-
aniline on hydrochloride of diazobenzene, and if the latter be
replaced by diazobenzenesulphonic acid, the above monosulphonic
acid is formed.

The base forms golden-yellow leaflets melting at 115°. Its
hydrochloride, Ci^HisNsjHCl, forms violet needles sparingly
soluble in water. The basic character of amidoazohenzene seems
to be increased by introduction of alcohol radicals into the amido-
group, as the salts of dimethylamidoazobenzene are far more
stable than those of amidoazohenzene. A dilute solution of the
base becomes reddened by a trace of acid, and on this fact
depends its application as an indicator in alkalimetry. Acetic acid
and amidosulphonic acids are without action on the compound.
Dimethylamidoazobenzene is sometimes used for colouring butter
and candles.

The monosulphonic acid forms brilliant violet needles, which
are sparingly soluble. Its salts are yellow, and mostly well
crystallised.

The calcium salt is obtained as a lustrous precipitate by adding
calcium chloride to a solution of the sodium salt.

The sodium salt of this sulphonic acid has been used as a

38 CHEMISTRY OP ORGANIC DYESTUFFS.

dyestuff under the names Tropaolin II, Orange III, and Heli-
anthine. It gives fine orange shades on wool and silk, but owing
to its sensitiveness towards acids has not met with great success.

Phenylamidoazohenzene [12],

CeH5-N=N-CeH,NHCeH5,

is formed by the action of diazobenzene chloride on diphenyl-
amine. It crystallises in golden-yellow prisms or leaflets.
M.P. 82°.

It is soluble in alcohol, ether, benzene, and ligroine, insoluble
in water. Acids colour the alcoholic solution violet, the salts
being precipitated as grey crystals. It dissolves in concentrated
sulphuric acid with a green colour, changing through blue to
violet on dilution with water. By action of amyl nitrite a nitros-
araine, M.P. 119°"5, is obtained. On reduction it yields aniline
and paramidodiphenylamine.

Phenylamidoazohenzenesul'phoniG Acid [12].

(1) (4)

HS03-CcH,N=N-C6H,NHC«H5.

(Tropaolin 00, Orange IV.)

Is obtained by action of p-diazobenzenesulphonic acid on an
acid, alcoholic, diphenylamine solution. The free acid forms
needles resembling graphite, which dissolve sparingly in water
with a red-violet colour. The salts are Avell crystallised, and, with
the exception of the insoluble calcium and barium salts, dissolve
easily in hot Avater, less easily in cold water. Concentrated
sulphuric acid dissolves the compound, forming a violet solution.
The sodium salt has a large application, and comes into commerce
under the above designations. It dyes wool and silk a beautiful
orange.

An isomeric compound prepared from metamidobenzene-
sulphonic acid is known as Metanil Yellow and dyes somewhat
yellower shades.

AMIDOAZO-COM POUNDS. 89

Yellow dyestuffs are also obtained by aetion of diazotoluene-
sulphonic acids on diphenylaminc.

Nearly all plienylamidoazo-eompounds yield nitro-derivatives
when their nitrosamines are carefully treated with nitric acid.
The nitro-group enters into the diphenylaminc, and certain
bodies obtained in this manner are used under the names Azo-
flavine, Citronine, and Indian Yellow. They are distinguished
from the original dyestuffs by their yellower shade.

Experimental trials have also been made with higher sulphonic
acids of pheuylamidoazobenzene.

Amidoazotoluenehenzene [1 3].

(1) (4) (1) (4)

QH,CH3-N = NC6H4NH2.

From paradiazotoluene and aniline. Forms long yellowish-
brown needles melting at 117°.

Amidoazhtoluenes.

(1) (2) (1) (3) (4)

A. C6H4CH3-N=N-C6H3CH3NHo. [13]

Is obtained from orthotoluidine in a similar manner to amido-
azobenzene from aniline. M.P. 100°.

(1) (4) (1) (S) (4)

B. C6H4CH3-N=N-C6H3CH3]SH2. [13]

From paradiazotoluene and orthotoluidine. M.P. 127-128°.

(1) (3) (1) (2) (4)

C. CyH.CHa-N^N-CcHsCHaNHa. [13]
From metatoluidine. M.P. 80°.

(1) (4) (1) (2) (4)

D. C«H,CH;}-N=N-C6H3CH3NH2. [13]

By the aetion of paradiazoamidotoluene on metatoluidine. M.P.
127°.

(1) (4) (1) (4) (2)

E. C6H4CH3-N=N-C«H3CH3NHo. [14]

By the interaction of paradiazoamidotoluene and paratoluidine.
M.P. 118°-5.

40 CHEMISTRY OF ORGANIC DYESTUFFS.

These amidoazotoluenes, -when treated with fuming sulphuric
acid, yield sul phonic acids, some of which are used as yellow
dyestuffs.

The first four amidoazotoluenes. A, B, C, D, contain the amido-
group in the para position to the azo-group. They are all reddened
by acids, and yield paradiamidotoluene on reduction.

The last compound, E, contains the groups in the ortho position ;
it is coloured green by acids, and yields orthodiamidotoluene on
reduction.

Amidoazoxylenes.

Seven isomeric amidoazoxylenes are known, but for a description
reference must be made to the literature of the sulyect [15, 16].

Generally speaking, their properties are similar to those of
amidoazobenzene and the amidoazotoluenes.

B'lamidoazohenzenes [12, 13].

A. Chryso'idine [17, 18].

(1)
(4) NHo

C6H4-N=N-C6H3 (.3)".
NH2

Chrysoidine is prepared by mixing equivalent quantities of
solutions of diazobenzene chloride and metaphenylenediamine.
The base crystallises from hot water in yellow needles, M.P.
117°"5. It dissolves sparingly in water, easily in alcohol, ether,
and benzene [18].

It forms two series of salts with acids [18] ; the monoacid salts
are stable and yellow in solution, the diacid salts are red and are
decomposed by water.

Ci2Hi3N4,HCl is obtained in two forms according to whether
it has been crystallised rapidly or slowly. In the first case it
forms long red felted needles, and in the latter anthracite black
aggregates of octahedrons possessing a green reflex. With an
excess of hydrochloric acid, Ci2Hi3N4(HCl)2 is obtained, a salt
soluble with a red colour, but decomposed by water.

AMIDOAZO-COMPOUNDS. 41

On reductiou chrysoidinc splits up, aniline and triamidobcnzene
being pi-oduced.

C12H11N4 (031130)2 is formed by warming chrysoidine with
acetic anhydride; forms yellow prisms, M.P. 250° [18]-

It yields a dimethyl derivative on warming with methyl iodide.

Tetramethylchrysoidine has been prepared by the action of
diazobenzene chloride on tetramcthylphenylenediamine.

A sulphonic acid may be obtained by treating chrysoidine with
fuming sulphuric acid, or by allowing paradiazobenzenesulphonic
acid to react with metaphenylenediamine.

Chrysoidine, which was discovered by Witt, is one of the few
basic azo-dyestuffs, and like all basic colouring-matters dyes cotton
mordanted with tannic acid. Its principal application is in cotton-
dyeing, especially for shading purposes. It gives a yellowish-
orange colour.

It is of historical interest, as being the first azo-dyestuflP pre-
pared by a direct synthesis.

B, Symmetrical Amidoazolenzene [19, 20].
Parazoaniline,

(1) (4) (1) (4)

Nn2-C6H4-N = N-C6H4-TsH2,

is formed by saponification of the acetyl compound described
below, and by reduction of the compound obtained by action of
paranitrodiazobenzene on aniline.

It forms long, flat, yellow needles. M.P. 140°.

It is sparingly soluble in water and benzene, easily in alcohol.

The moiioacid salts dissolve in alcohol with a green colour,
while the diacid salts give a red solution.

Acetyl derivative [20], Ci3lInN4(C2H30), is obtained by the
interaction of aniline and paradiazoacetanilide in presence of a
little hydrochloric acid. M.P. 212°. Its salts dissolve with a red
colour.

Di acetyl derivative, Ci2HioN4(C2H30)2, is formed on reduction
of paranitroacetanilide with zinc powder and alcoholic ammonia
[19]. It forms yellow needles. M.P. 282°.

42 CHEMISTRY OF ORGANIC DYESTUFFS.

Tetramethyl derivative [21],

(1) (i) (1) (4)

(Azyline), is formed by the action of nitric oxide on dimethyl-
aniline, and by action of paradiazodimethylaniline on the same
amine [22].

Diplienine of Gerhardt and Laurent [23] and liydrazoaniline
of Haarliaus [24] are regarded as hydrazo-compounds ; they are
probably diamidoazo-compounds, as they possess tinctorial pro-
perties in a marked degree, which is not usual in hydrazo-
compounds.

Triamidoazolenzene.

(1)

(1) (4) /NHj r-,^T

H2NC6H4-N = N-C,.H3< m [2o].
(Phenylene Brown, Vesuvine, Bismark Brown.)

Triamidoazobenzene forms brownish-yellow warty crystals,
wliicli dissolve sparingly in cold water, easily in bot water. M.P.
137°. Acids colour the brownish-yellow solution reddish brown,
and produce diacid salts.

Triamidoazobenzene is formed along with other azo-compounds,
on treating metapheuylenediamine with nitrous acid. Its hydro-
chloride forms the principal constituent of the dyestufFs known
under the above names. (A more recent view is that Bismark
brown consists partly at least of a compound of the formula

(1)

which is to be regarded as a metapheuylenediamine disazometa-
phenylenediamine.)

With the exception of chryso'idine, Bismark brown is the only
basic azo-dyestuflf in practical use. It is used in dyeing cotton and
leather.

Biamidoazotolucnes. [See 26, 27.]

AMIDOAZO-COMPOUXDS. 43

Benzeneamidoazonaphthalene [28, 29],

CgHsN = N - CioHyN Ho a,

is obtained by interaction of diazobenzene chloride and a-napli-
thylamine.

Sulphonic acids may be obtained by action of paradiazobenzene-
sulphonic acid on « and /3 naphthylamine.

A corresponding toluene compound has been prepared by action
of paradiazotoluene on a-naphthylamine [27].

The dyestuff known as orchil substitute or orseilline is prepared
by action of paranitrodiazobenzene on naphthionic acid (a-naph-
thylaminesulphonic acid). It produces reddish-brown shades on
wool and is dyed from an acid bath \_7'^'\ .

Amidoazonaph tlia lene,

aCioH,N=:N-CioH6NH2a [30],

is formed by action of nitrous acid on excess of a-naphthyl-
amine, and is best prepared by mixing a solution of two molecules
of a-naphthylamine hydrochloride with one molecule of sodium
nitrite. The base forms reddish-brown needles, which show a
green reflex; it melts at 175°, and is sparingly soluble in
alcohol, readily in xylene.

The salts dissolve in alcohol with a violet colour, and are
decomposed by water.

The azo-group is present in the a para position to the amido-
group.

Sulphonic acids of this compound are obtained by direct sulpho-
nation, or by combination of diazonaphthalenesulphonic acid with
a-naphthylamine.

A disulphonic acid of amidoazonaphthalene is obtained by
action of sodium nitrite on naphthionic acid ; its constitution
difters from that of the above acids, as the second a-positi >n
usually taken by the azo-group is occupied by the sulpho-group in
naphthionic acid.

The corresponding /3-amidoazonaphthalene is obtained in a
similar manner from /3-naphthylamiuc ; it melts at 156°, and is
a slightly weaker base.

Mixed amidoazonaphthalenes have also been prepared.

44 CHEMISTRY OF ORGANIC DYESTUFFS.

II. OXYAZO-COMPOUNDS.

Oxijazohenzene [31, 32, 33].

(1) w

C6H5-N = N-C6H,OH.

{Phenoldiazobenzene.)

Oxyazobenzene is prepared by interaction of diazobenzene
chloride and phenol-sodium [32], and is also formed by action of
barium carbonate on salts of diazobenzene [31].

It may further be obtained by treating the isomeric azoxy-
benzene with sulphuric acid [34], and by the action of nitroso-
phenol on aniline [33].

It forms needles, M.P. 151°; it is slightly soluble in water,
easily in alkalies and in alcohol.

Parasulphonic acid —

(1) (4) (1)

HS03-C6H4-N = N-C6H40H,

may be obtained by direct sulphonation, or by action of paradi-
azobenzenesulphonic acid on phenol-sodium.

This compound was formerly in commerce as Tropaolin Y, but
owing to its dull brownish shade was soon displaced. An isomeric
metasulphonic acid is formed by action of metadiazobenzenesul-
phonic acid on phenol-sodium [36] .

Dioxyazohenzene [35].

a. Unsymmetrical : —

(1)
/OH

CeH,N = N-CeH3<(3)
OH

This compound is prepared by action of diazobenzene chloride
on resorcin in presence of an alkali.

It forms red needles, M.P. 161° ; and is soluble in alcohol, ether,
and alkalies.

OXYAZO-COMPOUNDS. 45

Parasulplionic Acid.

HS03-CJI,-N=N-C6H3

OH
OH'

(Tropaolin O.)

This dyestuff is prepared by action of paradiazobenzenesulplionic
acid on resorcin [36, 37], and is also formed by sulphonation o£
dioxyazobenzene [37].

The free acid forms needles, which appear almost black with a
greenish lustre by reflected light, and red by transmitted light. It
is a strong acid, capable of liberating hydrochloric acid from a
solution of common salt, thereby forming a sodium salt.

The salts are orange-yellow, and are only decomposed by con-
centrated hydrochloric acid or by dilute sulphuric acid.

Tropaolin O is a strong dyestuff, producing a fine golden-
yellow shade on wool and silk, being dyed from an acid bath. It
was formerly used in silk-dyeing.

The metasulphonic acid is obtained from metadiazobenzene-
sulphonic acid and resorcin [36] .

/9. Symmetrical dioxyazohenzenes (Azqphenols) [38] : —

a. Fara-azophenol

is formed on melting paranitro- or nitrosophenol with potash,
M.P. 204°.

b. Ortlio-azojphenol

is formed similarly from orthonitrophenol, M.P. 171°.

Oxyazohenzenetoluene [33],
CH3C6H4-N=N-C6H,OH,
{Phenolazotoluene.)
is obtained from nitrosophenol and paratoluidine, M.P. 151°.

Cumen eazoresorcin^
(CH3)3C,H2-N=N-C6Pl3(OH)2,
from diazocumene and resorcin [39], M.P. 199°.

46 CHEMISTRY OF ORGANIC DYESTUFFS.

Amido-oxyazohenzene [40],

(1) (3) (1) (4)

H2NC6H4-N=N-C6H4(OH) (M.P. 168°),
is obtained by saponification of the acetyl-compound

C2H30NH-C6H4-N = N-C6H40H (M.P. 208°),

which is prepared by interaction of phenol-sodium and the diazo-
compound from monoacetylmetaphenylenediamine.

Oxyazo-compounds are also obtained by action of diazo-com-
pounds on the isomeric cresols [39, 41, 42] .

(x.-Azonaphflialene-resorcin [46],

CioH,-N=N-CJl3(OH)2,

forms red needles, M.P. about 200°.

Naphtholazo-dtestuffs.

These dyes belong to the oxyazo series, and have within the last
ten years attained enormous importance, on account of the beauty
of their shades and their strong tinctorial properties. For these,
and other reasons, they are worthy of being studied as a separate
class.

The isomeric naphthols combine with all diazo-compounds, pro-
ducing azo-compounds, and with a-naphthol

the azo-chain enters into the second a-position of the substituted
ring. This is exactly analogous to the formation of the corre-
sponding compounds with benzene derivatives containing a free
para position. The simplest a-naphthol azo-compounds are con-
stituted as expressed by the following formula :

OXYAZO-COMPOUNDS.

N=N—

/3-naphthol

has no free para position and the azo-group enters in the ortho
position, viz. in the adjacent a-position :

„— N=iSr-

The case is different when these positions are already occupied
by other groups, for example, by the sulpho-group. With a-napli-
tholthe azo-chain enters into the adjacent /S-position; for instance,
with o-naphtholsulphonic acid azo-compounds of the general
formula

3-N=N—

IISO,

are formed.

48 CHEMISTRY OF ORGANIC DYESTUFFS.

The formula with /3-naphthol :

« SO3H

is probably correct, but has not been proved to be absolutely
certain. In general, azo-compounds containing the chromophoric
and auxochromic groups in the ortho position are far more valu-
able as dyes than their allies of the para-series.

The latter have the undesirable property of altering their shade
on treatment with alkalies or acids in a much higher degree than
the former compounds. This applies equally to oxy- and amido-
azo-compounds, especially those of the naphthol series.

For this reason /S-naphthol gives more useful dyestuflPs than a-
naphthol.

The derivatives of the latter exhibit striking changes in colour
on treating with alkalies.

If, however, the para position in a-naphthol is substituted, as
in the a a-sulphonic acid, the azo-group enters in the yS- (ortho)
position, and stable and useful dyes are obtained. Diazo-compounds
are capable of reacting on /3-naphthol once, while a-naphthol, like
phenol, reacts with two molecules of a diazo-compound. In the
resulting dis-azo bodies the second azo-group is probably in the
/3 1 -position, as expressed in the following formula :

/3~N=N—

N=N-

The naphthol azo-dyes are almost exclusively applied in form of
their sulphonic acids. These may be obtained by combination of

OXYAZO-COMPOUNDS. 49

sulplionated diazo-compounds with naphtliols, or of diazo-com-
pouuds with naphtholsulphouic acids.

The sulpho-group of the diazo-compound has little or no influ-
ence in the shade of the dyestuff, but the isomeric naphtholsul-
phonic acids are capaljle of giving totally different dyestuffs with
the same diazo-compound. In most cases this may he attributed
to the different positions of the azo-group already mentioned. Tt
is necessary for a correct comprehension of the following dyestuffs
to consider the principal naphtholsulphouic acids somewhat more
closely, for although our knowledge in this direction is incomplete,
many valuable researches have been made in recent years, of which
those of Armstrong are especially worthy of mention.

At present three monosulphonic acids have been obtained from
a-naphthol, but the constitution of only one of these is known with
any degree of certainty. This is the a a-acid prepared by Nevile
and Winther, and studied more closely by Witt. It is obtained by
decomposition of the diazo-compound of naphthionic acid with
water, and from its method of formation is constituted according
to the formula :

SO3H

This formula agrees well with the nature of the dyestuffs
obtained from this acid ; they are totally different to the simple
a-naphthol dyes, as the azo-group enters in the /3 1 position and
not in the a 2.

The dyestuffs from a-naphthol and diazo-compounds of the
benzene series are orange or brown, while those from the a a-acid
are mostly of a beautiful ponceau-red tone.

A second acid was prepared by Schaeffer, in 1869, who probably
obtained it mixed with the a a-acid.

Schaeffer's acid is obtained along with the latter acid by heating
a-naphthol with concentrated sulphuric acid on the water-bath.
It differs from the a a-acid by the sparing solubility of its sodium-
salt in alcohol, and more especially by the dyestuffs it yields. These
are analogous to the corresponding a-naphthol derivatives, and
therefore very probably para-compounds.

50 CHEMISTRY OF ORGANIC DYESTUFFS.

The acid has probably the constitution expressed by the follow-
ing formula :

as it yields dinitronaphthol on treating with nitric acid^ and phthalic
acid on oxidation.

A third acid has been prepared by Baum, but little is known of
its constitution. [Patent, 1883, No. 3498, Provisional Specifi-
cation.]

Glaus and Oehler have examined an acid [75] to which they
ascribe the constitution a^ a^, but it is doubtful whether it is iden-
tical with the Schaeffer or with the Neviie-Winther acid.

It may be as well to take this opportunity of remarking that a
method often used for determining the constitution of najihthol-
sulphonic acids appears not to be trustworthy, as molecular changes,
which occur so frequently in the naphthalene series, appear to take
place here also. This is the method depending on the conversion
of the acids into chloronaphthalenes by means of phosphorus
pentachloride. Indeed the results so obtained often differ from
all others.

The Schoellkopf Aniline Co. have patented an acid obtained
by nitration of a-naphthalenemonosulphonic acid, reduction to
amido-acid, and conversion into naphtholsulphonic acid by the
diazo-reaction. It is so far characteristic as it gives a scarlet with
diazotoluene, while its isomers give oranges. [D.P. 15871.]

a-naphthol also yields a disulphonic acid (?), and a trisulphonic,
which, however, have no importance in the manufacture of azo-
dyes.

yS-naphthol, on treating with sulphuric acid, gives in the first
instance three monosulphonic acids.

One of these (the a-sulphonic acid or crocein-acid) is best ob-
tained at a low temperature. By further heating with sulphuric
acid it goes over into the yS- or Schaeffer's acid, which was pre-
pared by Schaeffer along time ago. These acids are distinguished

OXYAZO-COMPOUNDS. 51

principally by the different solubilities of their disodium com-
pounds :

p TT /SOgNa
<-ioH6xoNa •

The basic salt of the a-acid is easily soluble in hot alcohol,
while that of the Schaeffer acid is almost insoluble.

The third acid, which has only recently been identified by its
conversion into the corresponding yS-naphthylaminesulphonic
acid, is identical with the F- or S-acid. [Green : B. B. 1889,
p. 721.]

From the facts that azo-dyes from Schaeffer's acid differ but little
in shade and solubility from those obtained from /3-naphthol, and
that simple /3-naphthol azo-compounds on sulphonation always
yield derivatives of Schaeffer's acid, and never those of crocein-
acid, it may naturally be concluded that the azo-group enters in
the same position both in /S-naphthol and in Schaeffer's acid. This
is the Ui position.

The behaviour of the a-acid is totally different. The dyestuffs
do not resemble those from Schaeffer's acid and /3-naplithol in the
least, either as regards shade or solubility. Further, this acid may
easily be converted into a dinitro-compound with nitric acid, and
this is not the case with either /3-naphthol or Schaeffer's acid.
Another striking property of the a-acid is that its combination with
diazo-compounds takes place with much more difficulty than is
experienced with Schaeffer's acid. Its constitution is therefore

HSO,

justifying the designation /3-iiaphthol-a-monosuIplionic acid for
this acid. The conversion of the corresponding /3-naphthylamine-
sulphonic acid into a-naphthalenesulphonic acid also shows that
it is really an a-acid.

Schaeffer's acid yields sulphophthalic acid on oxidation, showing
that tlie hydroxyl and sulpho-groups are in different rings.

CHEMISTRY OF ORGANIC DYESTUFFS.

Noelting ascribes the following constitution to SchaefEer's
acid :

/3 HSO

A third sul phonic acid is that of Cassella and Co., prepared by
heating naplithalene-a-disulphonic acid with caustic alkali.

This acid is technically known as F-acid, and is identical with
the acid prepared by the diazo-reaction from Bayer's /3-naphthyl-
aminc-8-sulphonic acid.

Without doubt it has the constitution :

SO,Hi

It is without importance for preparing azo-dyes.

Of the ^-naphtholdisulphonic acids, three are used in the
colour-industry [73, 74] . Two of these are formed by energetic
action of sulphuric acid on yS-naphthol, and may be separated by
taking advantage of the different solubilities of their sodium salts
in alcohol or in concentrated salt-solution.

The acid soluble in alcohol and salt-solution (G-acid of Meister,
Lucius, and Briining, 7-acid of Cassella and Co.) behaves very like
/3-naphthol-a-monosulphonic acid (crocein acid), and must be
regarded as a derivative of the latter, as it is formed quantitatively
on further sulphonation of crocein acid. It may also be obtained
from Schaeffer's acid (this is contradicted by some chemists), and
Armstrong gives it the following formula : —

WSO,

HSO.

OXYAZO-COM POUNDS. OO

The azo-dycs from G-acid arc yellowish and easily soluble^ and
are very similar to those from the a-monosulphonic acid.

The disiilphonic acid from the sodium salt, sparingly soluble in
alcohol and salt-solution (R-acid, Meister, Lucius, and Briining),
gives dyestuffs of considerably bluer shade, and also more diffi-
cultly soluble. They are, however, very important.

This R-acid is best obtained by further sulphonation of Schaeffer's
acid, and it is also stated that G-acid is converted into R-acid on
heating with sulphonic acid. The constitution of the R-acid is
expressed by the formula : —

SO,H

Another disulphonic acid, ^-naphthol-8-disulphonic acid is
prepared by further sulphonation of the F-acid. It has the con-
stitution

SO,H

A yS-naphtholtrisulphonic acid is obtained by sulphonation of
/3-naphthol with fuming sulphuric acid at a high temperature. It
has been used for the preparation of azo-colours.

Azohenzene-a-naphthol [1],

CeH5-N = N-CioH«OHa,

is prepared by action of diazobenzene chloride on an alkaline
solution of yS-naphthol. It forms yellow leaflets, which dissolve
in alkalies with a violet colour.

54 CHEMISTRY OF ORGANIC DYESTUFFS.

Monosulplionic Acid [11].

(1) (4)

HS03-CoH,-N = N-C:oH60H a.
(Orange I. Tropaolin 000 No. 1.)

This dyestuff is prepared by action of paradiazobeuzene-
sulphonic acid on a-naplithol. The free acid forms almost black
leaflets, with a green reflex, which dissolve in concentrated
sulphuric acid with a violet coloration. Its alkali salts are orange-
yellow, and dissolve easily in water. The solutions become red
with excess of alkali (distinction from y8-naphthol dyestuff's).

The sodium salt is used in dyeing under the above names.

It dyes wool and silk in an acid bath, producing an orange
shade, which is somewhat redder and not so bright as that obtained
with the corresponding y3-iiaphthol orange. The calcium salt is
amorphous and insoluble. Owing to the sensitiveness which these
dyestuff's exhibit towards alkalies, the /3-naphthol derivatives are of
considerably more importance.

Azohenzene-^-naphthol [1].

C6H5N=N-CioHeOH.

Yellow leaflets, insoluble in alkalies.

Monosulplwnic Acids.

(1) (4)

i. HS03-C6H4-N=N-CioH60H/3.
(Orange II. Tropaolin 000 No.'^li)

From paradiazobenzenesulphonic acid and yS-naphthol. The
acid forms orange-yellow leaflets, soluble in water. The crystals
on drying lose water and fall to a powder resembling red lead.
The alkali salts are similar to the acid, and are unchanged by
excess of alkali (distinction from «-naphthol dyestuff's). Its
calcium salt dissolves sparingly, the barium salt not at all. The
compound dissolves in concentrated sulphuric acid with a magenta-
red colour. On wool and silk it gives a beautiful orange, and is
one of the most important azo-dyes.

OXYAZO-COMPOUNDS. 55

ii. CeHs-N^N-CioHsOHHSOg.
(Crocein Orange.)

From diazobenzene and Schaeffer's ^S-naphtliolmonosulphonic
acid (/S-acid). The shade of the dycstuff is somewhat yellower
than that of the former. It gives an orange-yellow solution with
concentrated sulphuric acid.

Disulphonic Acids.

^(HSOg).,

Orange G.

Is obtained by the action of diazobenzene on /S-naphtholdisul-
phonic acid (the modification G, soluble in alcohol). It is a
yellowish-orange dyestuff, which gives an orange-yellow solution
with concentrated sulphuric acid.

Scarlet 2 G.

This dyestuff is an isomer of the above, prepared by action of
diazobenzene chloride on the E modification of /5-naptholdisul-
phonic acid.

Amidoazohenzene'^-naphtholdisulphonic Acid.

(1) (4) //(H 803)2

HoN-C6H,-N=N-C,oH,^Qj|

May be obtained by saponification of its acetyl derivative, and by
combination of yS-naphtholdisulphonic acid (R) with paradiazo-
aniline [44] (from paraphenylenediamine and one mol. HNG^).
It forms brownish-yellow leaflets, which dissolve in alkalies with a
violet colour, becoming red with excess of alkali.

Acetyl derivative : —

C2H3O . HN-C^H.-N^-CioH^^ ^ M.

56 CHEMISTRY OF ORGANIC DYESTtFFS.

From p-diazoacetanilid and naphtholdisulphonicacid; forms red
leaflets.

DyestufPs obtained by combination of the diazotoluenes and
their sulphonic acids with /3-naphthol and its sulphonic acids are
also of technical value.

AZO-DTES FROM /3-NaPHTHOLDISULPHONIC AciDS AND THE
HIGHER HOMOLOGUES OF DiAZOBENZENE [45].

It has already been remarked on p. 53 that the isomeric
disulphonic acids of /S-naphthol give dyes of totally different
shades with diazo-compounds. This is probably caused by the
azo-group entering in a different position in the naphthalene
nucleus. This property is made use of in the colour-industry.
The acid corresponding to the sodium salt soluble in alcohol
(G-acid, Meister, Lucius, and Briining) gives orange-yellow dyes
Avith diazo-compounds of the benzene series, and scarlets with
those of the naphthalene series ; while the R-acid (Meister,
Lucius, and Briining), from the sodium salt insoluble in alcohol,
gives red dye-stuffs with the diazo-compounds of the benzene
series, varying in depth according to the molecular weight of the
latter [45].

The R-acid, when combined with the diazo-compounds of the
xylenes and higher homologues of benzene, gives rise to a series
of scarlet dyes, which have a wide application in wool-dyeing
under the names Ponceau R, RR, RRR, and G. a-diazonaphtha-
lene gives a deep claret-rcd (Bordeaux B). "With diazonaphthalene-
sulphonic acid and R-acid, a colouring-matter known as ''Ama-
ranth " is obtained. Orthodiazoanisol and its homologues give fine
red dyestuffs known commercially as Coccinines.

The dyes from diazo-compounds of the benzene series (Pon-
ceaux R, RR, RRR, and Coccinines) form scarlet powders, which
dissolve in strong sulphuric acid with a red colour. They give
crystalline calcium salts which are soluble in hot water. Dye-
stuffs containing naphthalene rests on both sides dissolve in
sulphuric acid with blue or violet colour.

OXYAZO-COMPOUNDS. o7

The following Table contains the most important dycstuffs
prepared from the uaphtholdisulphonie acids, excluding those
belonging to the tetrazo class, which are mentioned later : —

Ponceau 2 G (Meister, Lucius, & R-acid and diazobenzene.

Briining)

„ II (Badische Aniline- und So- R-acid and diazepam- and metaxy-

dafab.). lene (from coml. xylidiue).

„ 2 R (Actienges f. Aniline) . . R-acid and diazometaxylene (pure).

„ 3 R (Meister, Lucius, &Briin- R-acid and diazoetbylnietaxylene).

ing)

., 3 R (Bad. Aniline- und So- R-acid and diazopseudocumene.

dafab.).
„ 4 R (Actienges f. Aniline) . . Do.
„ 2 R (Meister, Lucius, & Briin- Do.

"'g)

JJordoaux B (do.) R-acid and diazonaplitbalene.

Amarantb (Cassella & Co.) R-acid and n-diazonapbtbalene-sulph.

acid.

Bordeaux S(Meister,Lucius,&Briining) Do.

Coccinin (Meister, Lucius, & Briining) R-acid and diazoanisol.

Pbenetol Red (do.) Do. and diazophenetol.

Auisol Red (do.) Dp. and homologues.

Orange G (Meister, Lucius, & Briining) G-acid and diazobenzene.

Ponceau 2 G (Bad. Anil. & Sodaf.) . . Do. and diazopseudocumene.

Crystal Ponceau (Cassella & Co.) .... Do. and a-diazonapbtbalene.

a-Azonaphthalene-(3-na2JhthoL

C10H7 — N — N2 — CioHgOH («-/3-oxyazonaphthalene) .

Is obtained by interaction of a-diazonaphthalene chloride and /3-
naplithol.

Monosidphonic Acid [47J.

HS03C:oH6-N = N-CioH60H.

(Fast Red, Roccelline.)

This is obtained by the action of a-diazonaphthalenesulphonic
acid on /3-naphthol,

The acid and its sodium salt both form brown needles, sparingly
soluble in cold water, easily in hot, separating from the hot
solution as gelatinous precipitates. The calcium and barium
salts are insoluble and amorphous. The compound possesses

58 CHEMISTRY OF ORGANIC DYESTUFFS.

very strong tinctorial properties, dyeing wool and silk red. The
shade is bluish and not particularly bright. It dissolves in con-
centrated sulphuric acid with violet colour, separating in brown
flocks on dilution.

Bisulplionic Adds.
i. CioHvN=N-CioH4^jfgQ^^^ [45].

a. Bordeaux B (Meister, Lucius, and Briining).
From ^-naphtholdisulphonic acid (insoluble in alcohol) and a-
diazonaphthalene. Gives a blue coloration with strong sulphuric
acid.

h. Crystal Scarlet (Cassella & Co.).

Obtained in a similar manner from a-diazonaphthalene and the
G- or 7-disulphonic acid (soluble in alcohol). The sodium salt
crystallizes very easily.

/OH
ii. HS03.CioH6-N=N-CioH5(

Crocein Scarlet 3 Bx.

From /3-naphthol-a-monosulphonic acid [48] and a-diazo-
naphthalenesulphonic acid. Is a beautiful scarlet dyestuff which
dissolves in sulphuric acid with a reddish-violet colour.

Sulplioazonaphthalene-u-naphtholsulphonic Acid.

/OH
HSOgCioHe-N^N-CioH^^HgQ^'

(AZORUBIX.)

This is prepared by combination of a-diazonaphthalenesulphonic
acid with the a-naphthol-a-sulphonic acid obtained from the former
acid by decomposition with water. It is a fine bluish-red dyestuff.
/8-naphthylamine and its sulphonic acids are also used in the
manufacture of dyestuffs. Oxyazonaphthalene, obtained from /3-
diazonaphthalene and /3-naplithol, is known as " Carminnaphthe/^
and is used in colouring varnishes.

/8-naphthylaminesulphonic acid (Bronner's acid), prepared by
heating Schaeffer's yS-naphtholmonosulphonic acid with ammonia.

AZO-COMPOUNDS. 59

gives wlien diazotised and combined with /S-naphthol, a dyestuff
used in silk-dyeing. With a-naphthol-a-sulphonic acid the dye
known as Brilliant Scarlet is obtained.

A dyestutf known as Silk-red, or Scarlet for Silk, is prepared
by sulphonating yS-naphthylamine and diazotising the resulting
sulphonic acid and combining with /9-naphthol.

III. AZO-DYES FROM DIAZOCARBONIC ACIDS.

Diazo-compounds combine with phenols and amines to form azo-
compounds. The tinctorial properties of these bodies are generally
weak, becoming intensified, however, by converting the carbonic
acids into their ethers.

Bimethjlamidohenzene-azo-henzoic Acid [50].
COOHC6H4-N=N-C6H4N(CH3)2.
Is obtained from m-diazobenzoic acid and dimethylaniline.

Phenolazo-meta-henzoic Acid [49].
COOHC6H4-N = N-C6H40H.
From diazobenzoic acid and phenol. M.P. 220°.

0-Sulphonic Acid.
From o-phenolsulphonic acid and m-diazobenzoic acid.

BesorciTi-azo-henzoic Acid [49].

(1) 3 /OH

COOH-CeH4-N = N-CeH3CQjj-

^Wa^hthol-azo-henzoic Acid [49].

(1) (3) j3

COOHC6H4-N = N-Ci,H«OH.

M.P. 235°. Ethyl ether, M.P. 104° (from diazobenzoic acid
ether and /3-naplithol) .

60 CHEMISTRY OF ORGANIC DYESTUFFS.

Monosulphonic Acid [49].
COOHCeH^-N^NCioH^ggQ^.

From m-diazobenzoic acid and /3-naphtholmonosulphonic acid.

Disulphonic and trisulphonic acids have also been prepared by
action of m-diazobenzoic acid and its sulpho-acids on yS-naphthol-
disulphonic acid. Diazoanisic acid, as well as the paradiazocin-
namic acid and its ethers [51], gives red azo-dyes [49] with
naphthol acid and its sulphonic acids.

IV. AZO-DERIVATIVES FROM CARBONIC ACIDS AND
DIAZO-COMPOUNDS.

Oxy- and amidocarbonic acids combine with diazo-compounds
to form azo-dyes, some o£ which possess the property of dyeing on
metallic mordants.

Azolenzene-dimethylamidohenzoic Acid [50, 39].
C«H, . N=:N-C«H,

/N(CH3)2

.ex.5.- X, -6-3^^^Qjj .

From diazobenzene and dimethyl-m-amidobenzoic acid. M.P.
125°.

Bimethylamidohenzoic Acid-azolenzoic Acid.

/COOH
C00HCeH,-N=N-CeH3/ ^^^ ^ [49].

N (CHaja

By action of m-diazobenzoic acid on m-dimethylamidobenzoic
acid.

Azo-S-diamidobenzoic Acid'^p-benzenesulphonic Acid [9].
HS03-CeH,-N=N-C6H3:;

COOH

Is prepared by action of p-diazobenzenesulphonic acid on S-di-
amidobeuzoic acid.

AZO-COMPOUNDS. Gl

Azohenzenesalicylic Acid [52].

CeH5N=N-C6H3

(1)
/OH (2)

'\cooh'

From diazobenzene and salicylic acid.

Monosulphonic Acid.
From p-diazobenzenesulphonic acid and salicylic acid [3G].

Azonaphthalene-salicylic Acid [53].

/OH

CioH7N=N-C6H3:f

From a-diazonaplithalene and salicylic acid. DyestufFs have
also been prepared from salicylsulphonic acid and diazo-compounds
[54]. Meta- and para-oxybenzoic' acids [36], as well as oxy-
naphthoic acids [55], give colouring-matters with diazo-compounds.

The dyes prepared from salicylic acid mostly possess the
property of dyeing on alumina, iron, and chromium mordants, in
a similar manner to alizarin.

This property, which is not met with in the meta- and para-
oxy-derivatives, seems to be connected with the ortho position, as
in the quinoneoxime dyes.

These mordant-dyeing properties are found in a much higher
degree in the bodies obtained by action of nitrodiazo-compounds
on salicylic acid (Germ. Pat. 44170, 16 Nov., 1887). The dye-
stuff from metanitrodiazobenzene and salicylic acid comes into
commerce as Alizarin Yellow G, and produces a fine yellow lake
with chromium oxide. The pure dyestuff crystallizes from alcohol
in light yellow needles. M.P. about 230°. Its constitution may
be expressed by the formula : —

/COOH
CeH,N02-N=N-CeH3(^^ .

It has been used to a certain extent in calico-printing as a
substitute for Persian-berry extract and fustic extract. An

62 CHEMISTRY OP ORGANIC DYESTUFFS.

isomeric compound from paranitrodiazobenzene is known as
Alizarin Yellow E, and gives more orange shades in dyeing.

These compounds are also useful in wool-dyeing. The dyeing
process is simple, as owing to the stability of these compounds the
mordanting with bichromate and the dyeing may be effected in one
bath, a-oxynaphthoic acid combines with nitrodiazo-compounds,
producing brown dyestuffs which possess the property, like the
above, of dyeing on mordants.

V. TETRAZO- OR DISAZO-DYESTUFFS.

These bodies differ from the simple azo-compounds by con-
taining the azo-group — N=N — more than once in the molecule.

According to their method of formation and constitution, these
compounds may be divided into different classes. The first of
these classes, the type of which is phenolbidiazobenzene discovered
by Griess, contain the two azo-groups and the auxochrome amido-
or hydroxyl groups in one benzene nucleus. These compounds
are obtained by the action of diazo-compounds on oxy- or amido-
azo-compounds.

A second class contains only the azo-groups in one ring, while
the auxochrome is in another. They may be prepared by acting
upon amines or phenols with diazoazo-compounds (from amido-
azo-bodies), or by diazotisation of diamines and subsequent com-
bination with amines or phenols [43, 46].

A third class of tetrazo-dyestuffs includes those prepared from
benzidine and its analogues. These contain two azo-groups in two
different rings, which are linked to each other. Tertiary and
quaternary azo-compounds, i. e., those containing three and four
azo-groups, have also been obtained.

Phenoldisazohenzene (Phenolhidiazohenzene) [28, 56],
C6H5N=N-C6H30H-N = N-C6H5.

Is prepared by treating diazobenzene nitrate with carbonate of
barium, or by the action of the former on oxyazobenzene.

It forms brown leaflets, M.P. 131°. A homologue, M.P. 110°,
may be obtained from paradiazotoluene and oxyazobenzene [56] .

TETRAZO-COMPOUNDS. 63

Besorcindisazohenzene [46].

C6H5-N2~C6H2(OH)2-N2-C6H5.

Two isomeric compounds are formed by the action of diazoben-

zene chloride on metadioxyazobenzene.

«. Soluble in alkalies, M.P. 215°.

/3. Insoluble in alkalies, M.P. 222°.

p-diazotoluene reacts with m-dioxyazobenzene, three isomeric

resorcindisazotoluenebenzenes being formed [46].

o 1 ui • 11 r fa. M.P. 196°.

Soluble m alkalies < i\/rT> o^io

(.Oi. M.P. 241 .

Insoluble in alkalies yS. M.P. 198°.

Various disazo-compounds of this class may be obtained from
azotolueneresorcin (from p-diazotoluene and resorcin) by action
of diazobenzene and diazotoluene [46].

Amido-derivatives are produced by action of diazo-compounds
on unsymmetrical diamidoazobenzene (chrysoidine) and its homo-
logues.

For example, chrysoidine and diazobenzene chloride react to
form azobenzenephenylenediaminebenzene [57] . M.P. 250°.

C«H5-N = N-C6H2(OH3)3-N=N-C6H5.

Homologues and carbonic acids of these bodies have also been
prepared [57, 58].

AZO-DYES FKOM AmIDOAZO-COMPOUNDS.

Amidoazo-compounds, of which the simplest representative is
amidoazobenzene, are converted into the corresponding diazoazo-
compounds, which latter, like simple diazo-compounds, react with
amines and phenols, azo-dyes being formed. Amidoazosulphonic
acids behave in the same way.

Benzenetetrazobenzeneplienol {Tetrazohenzenephenol) [59].

1 4 1 (4)

C6H5-N=N-C6H4-N = N-C6H,OH.

Is formed by interaction of diazoazobcnzene and phenol. It may
be regarded as the simplest representative of this class.

64 CHEMISTRY OF ORGANIC DYESTUFFS.

Benzenedisazohenzene-ji'naphthol [60].

C6H5-N=N-C6H4-N = N-CioHcOH.
( Tetrazobenzene-^- naphth ol. )

From diazoazobenzene and yS-naphthol. Forms a brick-red
powder or brown leaflets with a green reflex. It is insoluble in
alkalies, sparingly soluble in alcohol, easily in hot glacial acetic
acid. It gives a green solution with concentrated sulphuric acid.

The sulphonic acids of this compound come into commerce as
Biebrich and Crocein scarlets, according to the position of the
sulpho-group.

Monosulphonic Acid [60].

(1) (4) (1) (4) 3

HS03C6H,N = N-C6H4N=N-CioH60H.

From diazoazobenzenemonosulphonic acid and /3-naphthol. The
sodium salt forms red needles or an amorphous red powder which
is sparingly soluble in cold water, more easily in hot water. The
hot aqueous solution on cooling solidifies to a gelatinous mass.
The calcium and barium salts are insoluble.

Bisulphonic Acids.

A. HS03C6H4N=N-C6H3HS03N=N-C:oH60H [60].

(Biebrich Scarlet.)
From diazoazobenzenedisulphonic acids and /3-naphthol.
The sodium salt is easily soluble, and forms a thick syrup with a
small quantity of water, becoming crystalline on long standing.
It may be crystallized from dilute alcohol in red needles. The
calcium and barium salts are insoluble.

Commercial Biebrich scarlet is generally this disulphonic acid,
sometimes it contains the monosulphonic acid also. Both give a
green solution with concentrated sulphuric acid. The shade
obtained on wool and silk is a beautiful cochineal scarlet.

B. HS03-CeH4-N=N-CeH,N=N-CioH50H. HSO3.
The isomeric monosulphonic acids of yS-naphthol react with di-

azobenzenesulphonic acid, producing dyes which, however differ
greatly according to the position of the sulpho-group. Schaefier^s
yS-acid gives dyes of a bluish shade and of little value, while the a-
acid gives dyestufis the shade of which is much superior to that of
Biebrich scarlet.

TETRAZO-COMPOUNDS. 65

This body [01] is known as Crocein Scarlet 3B, and although
not producing fast shades is used in cotton-dyeing. Crocein
Scarlet 7 B is a dyestuff of somewhat bluer shade, and is obtained
from orthoamidoazotoluenesulphonic acid in the same manner.
The tetrazo-dyes prepared from /3-naphthol-a-sulphonic acid give
soluble crystalline calcium salts, while those from the other acid
give amorphous and insoluble calcium salts.

The G-disulphonic acid behaves similarly to the a-acid, and its
combination with diazoazobenzene, known as Brilliant Crocein M
(Cassella & Co.), is closely allied to Crocein 3 B. All the naph-
thol azo-dyes derived from amidoazobenzene and its homologues
give a characteristic reaction on reduction, which readily serves for
their recognition. On warming the alkaline solution with zinc
powder, only the naphthol or its sulphonic acid is split off ; the
amidoazo-compound being regenerated.

Another characteristic property of the compounds of this class is
that they exhibit a peculiar behaviour towards strong sulphuric acid.

The sulphonic acids containing the sulpho-groups in the ben-
zene rings only react like the non-sulplionated azo-compounds,
giWng a green colour with concentrated sulphuric acid; if the
sulpho-groups are in the naphthalene ring, a violet colour is
obtained ; while, if both rings are sulphonated, the colour is pure
blue. On warming the green solution of benzene-disazobenzene-
yS-naphthol in sulphuric acid, the colour gradually changes to
blue, and the sulphonic acid formed is identical with the one from
diazoazobenzenemonosulphonic acid and /3-naplithol-/3-monosul-
phonic acid.

a-naphthylamine reacts with diazoazobenzenedisulphonic acid
to produce a brown dyestuff, which is known as Archil Brown,
possessing, however, no great importance.

The combination of diazoazobenzenedisulphonic acid with
])aratolyl-/3-naphthylamine is known as Wool-Black.

Azodibenzenephenylenediamine [57].
CeH,N=N-CeH,-N=NCeH3(NH3)2.

Is formed by action of diazoazobenzene chloride on metapheny-
lenediamine. It forms brownish-red needles, which melt at 185°,
and are easily soluble in chloroform, benzene, ether, and alcohol.

CHEMISTRY OF ORGANIC DIESTUFFS.

Azodibenzenetoluylenediamine [57].
CcH5N=N-CeH,N = N-C,H5(NH2)2.

From diazoazobenzene chloride and metatoluylenediamine.
Forms light brown needles. Sulphonic acids of this compound
are formed by using diazoazobenzenesulphonic acids.

Azohenzeneazoparacresol [42].

C6H,N=N-C6H,N = NC6H3^^^

Is formed by action of diazoazobenzene chloride on paracresol.
It forms brown needles, M.P. 160°, and dissolves in sulphuric acid
with violet colour.

The diazoazonaphthalenes combine with sulphonic acids of the
naphthols to form dyestufiFs, some of which are used on a large,
scale.

Diazoazonaphthalenesulphonic acid, obtained by combination
of /S-naphthylaminesulphonic acid and a-uaphthylamine, reacts
with naphtholsulphonic acids, producing deep blue dyestuffs. One
of these comes into commerce as Blue-black or Azo-black, and dyes
wool a shade similar to that with nigrosine [68] .

Other dyestuffs derived from amidoazo-compounds are com-
prised in the following table : —

Dyestuff.

Diazotised Base.

Combined with

Jet-Blac]{ K

Benzenedisulplionic acid
azo-a-naplithylamine.

Plienyl-a-naphthylamine.

Fast Violet Bluish ..

/3-toluenesulphonic acid

^-naphthol'/S-sulpliomc

azo-a-uaplithylamine.

acid.

Diamond Black ....

Salicylic acid azo-a-

a-naphthol-a-sulphouic

naplithylamine.

acid.

Naphthylamine Black

Naphthalenedisulphonic

a-naphthylamine.

acid azo-a-naphtliyla-
mine.

Brilliant Black

Am idoazonaptthalene-

^-naptholdisulphonic acid

disulpliouic acid.

Meldola introduced a general method for preparing disazo-
compounds [63]. Nitrodiazo-compounds are combined with

TETRAZO-COMPOUXDS. 67

plicnols or amines ; the nitro-group is tlicn reduced, and the
resulting amido-compound may be diazotised and again combined
with an amine or a phenol. As au example of the method of
procedure the following is cited.

Paranitrodiazobenzene combines with diphenylamine to pro-
duce :

N02-C6H4-N=N-C6H4NH-C6H5.

This body on reduction yields:

NH2-CJI,-N = N-C«H4NH-CeH5.

This may be diazotised, and on combination with /3-naphthol
yields :

yS-OH-Ciori«-N=N-CeH4N=NCoH,NH-C„H5.

The dyestuffs obtained in this manner belong to the same series
as those prepared with the diazo-compounds of paraphenyleue-
diamine.

The nitroazo-compounds obtained by combination of nitrodiazo-
compounds with primary amines maj^ be diazotised and combined
with phenols ; resulting nitrodisazo-compounds on reduction
yield amido-compounds, wliicli, Avlien again diazotised and com-
bined with a phenol, yield tertiary azo-compounds, containing
three azo-groups.

Paranitrodiazobenzene combines with a-naphtliylamine, form-
ing:

NOo - CcH^N = N - CioHcNIl2 a.

This body, on diazotising and combining with /3-naphthol, yields :

N02-CcH4-N = N-Ci,He-N=N-CioH«OH;S.

On reduction of the nitro-group, and treating with nitrous acid,
a diazo-compound is obtained, which with yS-naphthol yields a
tertiary azo-compound : —

HOCioH6-N=N-CcH,N = N-C„He-N = NCioH60H^.

Numerous azo-compounds were prepared in an analogous
manner, and for these reference must be made to the original
article [62],

68 CHEMISTRY OF ORGANIC DYESTUFFS.

AZO-DYES FROM BENZIDINE AND ANALOGOUS BaSES.

The tetrazo-compounds obtained from benzidine and similar
bases comljine with phenols and amines to produce yellow, red,
blue, and violet dyestuffs. These have attained considerable
importance on account of their remarkable property of dyeing (in
form of alkali salts) on unmordanted vegetable fibres.

The credit of this discovery belongs to P. Griess, who first
remarked on it in his English patent (1884, No. 1099).

Tetrazodiphenyl combines with naphthionic acid, producing a
dyestuflF: —

which has considerable application under the name " Congo
Red" [64].

The f ree sulphonic acid is blue, the salts are scarlet, and give the
same shade on cotton. These shades, though fast to soap, are
unfortunately turned blue by weak acids. This property is less
marked in the dyestuff known as Benzopurpurine B. It is
obtained [69] from tetrazoditolyl (obtained from o-tolidine and
nitrous acid) and the /3-naphthylaminesulphonic acid, obtained
by Bronner from SchaefiFer's /9-naphtholsulphonic acid and
ammonia.

It will be of interest, before entering into the consideration of
these dyestuffs, to examine the constitution of the naphthylamine-
sul phonic acids.

The sulphonic acids of a- and yS-naphthylamine are used for
production of azo-dyes in general, their principal application being
in the manufacture of the direct-dyeing cotton- colours.

They are produced technically by two methods, either by direct
sulphonation of the naphthylamines or by heating the naphthol-
sulphonic acids with ammonia (i.e., a compound yielding ammonia
on heating).

TETRAZO-COMPOUNDS. 69

As the iiaplithylamincsiilphonic acids are very numerous, only
those of technical value will be considered here.

Only one of the sulphonic acids of a-naphthylamine, the so-
called naphthionic acid, is of importance.

I. Sulphonic Acids of u-naphthylamine.
Naphthionic acid, CiyHg^^ p.,

SO,H

This acid is prepared by heating one part of a-naphthylamine
with three to five parts of concentrated sulphuric acid at 100°, or
by heating a-naphthylamine sulphate to 180°-200°.

II. Sulphonic Acids of ^-naphthylamine.

By the action of concentrated sulphuric acid on y8-naphthyl-
amine two monosulphonic acids are first formed, /3-naphthylamine-
a-sulphonic acid (corresponding to the crocein acid from /3-naph-
thol), and the yQ-uaphthylamine-7-sulphonic acid.

At a higher temperature two other acids are formed, the
/9-naphthylamine-yS-sulphonic acid (Bronner's acid corresponding
to the Schaeffer acid from yS-naphthol), and /3-naphtlilyamine-
F-sulphonic acid, corresponding to the F-acid. from /3-naphthol.
The /3- and F-acids are not products of direct sulphonation, but
result from a molecular change in the a- and 7-acids, as both
these acids, when heated with sulphuric acid, go over into a
mixture of Bronner and F-acid. This mixture was termed 5-ju;id^
and its discoverers, Bayer and Duisberg {70], and somewhat later
Weinberg {Jl], showed that it could be split up into two acids — the
Bronner and the F-acids. These yS-naphthylaminesulphonic acids
may also be produced by heating the corresponding naphthol-

CHEMISTRY OF ORGANIC DYESTCJFFS.

sulphonic acids with ammonia {i. e., a compound j'ielding ammonia
on heating). In this manner the crocein acid yields /3-napthyl-
amine-a-sulphonic acid, Schacffer's acid yields yS-naphthylamine-
/3-sulphonic acid, and tlie F-acid of Cassella yields the corre-
sponding /3-naphthylamine F-acid.

As yet the /3-naphtholsulphonic acid corresponding to y8-naph-
thylamine-7-sulphonic acid has not been isolated from the acids
formed in sulphonating /3-naphthol. The constitutions of the
acids, according to the most recent researches, may be graphically
demonstrated by the following formulae : —

SO,H.

Nil,

SOJI

NIL,

a-acid.

/3-acid (Bronner)

NH,

SO,IJ

NH,

SO3H

y-acid.

F-acid,

Of these sulphonic acids the j6- and F-acids produce fine red
dyestuffs with tetrazo-compounds, while the a- and 7-acids give
worthless yellow ones.

As has already been stated, the yS-acid is used in the manufac-
ture of Benzopurpurine B, and the F-acid serves, in combination
with o-tetrazoditolyl, for production of a sparingly soluble, bluish-
red dyestuff, known as Diamine-red 3 B.

If a mixture of both acids {i. e. the so-called S-acid) is used, a
fine mixed dyestuff is produced, which contains one molecule of
each acid linked to the benzene chains of the ditolyl. This body
forms the principal constituent of the dyestuff known as Deita-
Purpurine 5 B. Mixed dyestuffs of this class are easily obtained,
on account of a peculiar property of the tetrazo-compounds. The

TETRAZO-COMPOUXJ)^ 71

diazo-groups do not react simultaneous iv w-i'n the amine or
phenol. The second diazo-group combines with some difficulty,
and indeed the action is frequently aided by warming. Some of
these dyestuffs are commercial products.

/3-naphtholdisulphonic acid (R-acid) and a-naphthol-o-sul phonic
acid both combine with tetrazodiphenyl and tetrazoditolyl, forming
blue dyestuffs, which dye directly oq unmordanted cotton.

The dyestuff from tetrazoditolyl and o-naphthol-o-sul phonic
acid is known as Azo-blue, and produces reddish-blue shades on
coiton, which are, however, fugitive to light [63] .

A more stable dyestuff, which possesses at the same time a
purer shade, is obtained from dimethoxylbenzidine,

CHjOCeHjXHj

I
CHaOCeHsNHj

and a-naphthol-a-sul phonic acid. It comes into commerce as
Benzazurine [70].

The combination of tetrazodiphenyl and salicylic acid is known
as Chrysamine [66]. It produces on cotton a somewhat sad
yellow, and serves principally for production of the cream shades
used as groundwork in calico-printing.

Tetrazostilbene (obtained by reduction of azoxystilbene and
diazotisation of the resulting diamidostilbenej and its sulphonic
acids yield numerous dyestuffs, some of which are capable of
industrial application. Hessian Yellow, for example, is obtained
bv combining tetrazostilbenedisul phonic acid with salicylic acid.

The dyestuffs of this class have the property of acting to a
certain extent as mordants for basic dyestufis, and cotton dyed
with them acts with basic dyestuffs as if prepared with tannic
acid. Frequent application of this property is made in practice.
For instance, methylene blue, green, &c., may be dyed on a blue
azo-dvestuff, and in this manner the shades may be modified at
will. '

The following Table comprises the principal direct dyes at
present in the market : —

CHEMISTRY OF ORGANIC DYESTUFPS.

Dyestuf.

Diazotised Bade.

Combined with

Chrysamine G

Benzidine.

2 mols. salicylic acid.

Benzo-Orange G R . .

1 mol. salicylic acid.
1 mol. naphthionic acid.

Congo Yellow Paste

1 mol. sulphanilic acid.
1 mol. phenol.

Congo Red

2 mols. naphthionic acid.
1 mol. naplithionic acid.

Congo Corinth

(

1 mol. o-naphtholsulphonic

acid N.W.
1 mol. /3-naphthylamine-

Brilliant Congo G . .

■ )

disulphonic acid R.
1 mol. /3-naphthylamine-
monosulphouic acid B,

Deltapiirpurine G . . . .

>»

2 mols. /i-naphthylamine-
8-monosulphonic acid.

Azo-orseilline

2 mols. a-naphtholmono-
sulphonic acid N.W.

Benzidine Blue

2 mols. /8-nai)htholdi8ul-
phonic acid R.

Bordeaux Extra ....

1 "

2 mols. /3-naphtholniono-

Congo Violet

sulphonic acid li.

2 mols. amidonaphthobul-
phonic acid prepared

Diamine Black R . . . .

from /3-naphth3^1amine-'y-
disulphomc acid by melt-

I
1

ing with alkali.
1 mol. y-amidonaphthol-

Diamine Faf>t Red . .

sulphonic acid.
1 mol. salicylic acid.

Diamine Violet N . . . .

2 mols. -y-amidonaphthol-
sulphonic acid.

Chrysamine R

Orthotolidine.

2 mols. salicylic acid.

Congo Red 4 R ....

{

1 mol. naphthionic acid.

1 mol, resorcin.

1 mol. naphthionic acid.

Congo Corinth B . . . .

(

1 mol. a-naphtholsulphonic

acid N.W.
1 mol. /3-naphthylamine-

Brilliant Congo R . .

■ J

sulphonic acid B.
1 mol. /3-naphthylamine-
disulphonic acid R.

Benzopurpurine B . .

2 mols. |8-naphthylamine-
monosulphonic acid B.

Benzopurpurine 4 B. .

)»

2 mols. naphthionic acid.

Benzopurpurine 6 B . .

2 mols. naphthylamine-
monosulphonic acid
(Laurent).

1 mol. /3-naphthylamine-

Delta-Purpurine 5 B .

" 1

8-monosulphonic acid.

1 mol. /3-naphthylamine-

monosulphonic acid B.

TETRAZO-COMPOUNDS.

Table {continued).

Dyestuff.

Delta-Purpurine 7 B.
Diamine Red 3 B. . .
Rosazurine B

Rosazurine G

Azo-Blue

Toluylene Orange G .
Toluylene Orange R ,

Brilliant Purpurine .

Direct Red

Cotton Red

Sidphonazuriue .

Rosazurine BB .
Diamine Red NO.

Diamine Yellow N . .

Diamine Blue B . . . .

Diamine Blue 3 R . .
Diamine Black B. . . .

Diamine Blue-Black E

Benzopurpurine 10 B
Rosazurine

Benzoazurine G

Diazotised Base.

Orthotolidine.

Diamidophenyltolyl.

Orthometatolidine.

Benzidinesulphoue di-

sulplionic acid.

Benzidinesulphoue.

Etlioxybenzidine. ^

Diauisidine.

Combined with

2 mols. /3-naplithylamine-

S-monosulphonic acid.
2 mols. methyl-/3-naphthyl-

amine-5-mouosulphonic

acid.
1 mol. metliyl-/3-naplithyl-

amine-8-monosulphonic

acid.

1 mol. ^-naplitliylamine-8-
monosulphonic acid.

2 mols. a-naphtholsulphonic
acid N.W.

1 mol. cresotic acid.

1 mol. metatoluylenedia-
minesulphonic acid.

2 mols. metatoluylenedia-
minesulphonic acid.

1 mol. /3-naphthyIamine-
disulplionic acid II.

1 mol. naphthionic acid.

2 mols. naphthionic acid.
2 mols. naphthionic acid.

2 mols. phenyl-j3-naphthyl-
amine.

2 mols. naphthionic acid.

1 mol. /3-naphthylamine-
SLiIphonic acid B.

1 mol. /3-naphthylamine-
sulphonic acidF.

1 mol. salicylic 1 The pro-
acid. > duct is then

1 mol phenol. | ethylated.

1 mol. ^-naphthol-5-disul-
phonic acid.

1 mol. a-naphthol-a-sul-
phonic acid.

2 mols. a-naphthol-a-sul-
phonic acid.

2 mols. -y-amidonaphthol-
monosulphonie acid.

1 mol. /3-naphthol-8-disul-
phonic acid.

1 mol. y-amidonaphthol-
sulphonic acid.

2 mols. naphthionic acid.

2 mols. /S-iiaphtliylamine-
sulphonic acid B.

2 mols. a-naphtholsul-
phonic acid N. W.

CHEMISTRY OF ORGANIC DYESTUFFS.

Table {continued).

Byestuf.

Diazotked Base.

Combined with

Benzoazuriue 3 G

Dianisidine.

2 mols. a-naphthylaniine-
sulphonic acid (Cleve).

Brilliant Azurine 5 G

2 mols. dioxynaphthalene-
monosulphonic acid from
Schollkopf's acid.

1 mol. naphthionic acid.

Azo-Violet

1 mol. a-naphtholsulphonic
acid N.W.

Heliotrope

2 mols. methyl-/3-napbthyl-
amine-8-sulplionic acid.

Hessian Yellow ....

Diamidostilbenedisul-
phouic acid.

2 mols. salicylic acid.

Brilliant Yellow

Diamidostilbenedisul-
phonic acid.

2 mols. phenol.

Chrysopheniue

Ethylation of

Brilliant Yellow.

Hessian Purple N . . , .

Diamidostilbenedisul-
phonic acid.

2 mols. /3-naphthylamine.

Hessian Violet

Diamidostilbenedisul- \

1 mol. a-naphthylamine.

phonic acid. (

1 mol. /3-naphthol.

Carbazol Yellow ....

Diamidocarbazol.

2 mols. salicylic acid.

Naphthylene Red . .

\-~i naphthylenedia-
mine.

2 mols. naphthionic acid.

Salmon Red

Diamido-diphenylene.

2 mols. naphthionic acid.

Cotton Yellow

2 mols. salicylic acid.

Saint Denis Red ....

Diamido-azoxytoluene.

2 mols. naphtholsulphonic
acid N.W.

Jienzo-Browo B ....

Trianiido-azobenzene.

Naphthionic acid.

Benzo-Blue-Black G

Benzidinedisul phonic

2 luols. a-naphtholsul-

acid disazo-a-naph-

phonic acid N.W.

thylamine.

Benzo-Blue-Black R

Tolidine disazo-a-naph-

2 mols. a-naphtholsul-

thylamine.

phouic acid N.W.

Benzo-Black

Benzidine disazo-sali-

2 mols. a-naphtholsul- i
phonic acid N.W.

cylic acid a-naphthy-

lamine.

The property possessed by the above dyestuflFs of becoming
fixed on cotton from an alkaline bath (in form of their salts) is
not^ as has been supposed, peculiar to the derivatives of benzidine
and its analogues. This characteristic is far more widely distri-
buted, and has only been overlooked. Nearly all tetrazo-com-
pounds may be fixed to a slight extent on cotton, and the dyestufi's
obtained from paraphenylenediamine are almost as capable in
this respect as the benzidine derivatives.

AZO-COMPOUNDS. 75

Azarin aS [67].

The sodium bisulphite compound of an azo-dycstuff, prepared
hy combining diclilordiazophenol with yS-naphthol, comes into
ommerce under the above designation.

This azo-dyestuff, which is insoluble, has a fine red colour, and
possesses the property of forming a lake with alumina. By treat-
ment with sodium bisulphite this body, like all azo-dyestuffs,
yields an unstable sulphonic acid, which is only slightly coloured.
If this compound is printed with aluminium acetate, and steamed,
the sulphonic acid is decomposed, and the dyestuff combines with
the alumina to a firmly adhering lake.

Azarin finds its principal application in calico-printing, and
produces a fine red which, though fast to washing, is not sufii-
ciently fast to light to compete with alizarin.

Another azarin is obtained by combination of diazotised dia-
midooxysulphobenzide (phenolsulphone) with yS-naphthol. It is
also applied in form of its bisulphite compound.

Sun- Yellow.

Another dyestuff closely related to the azo-compounds is a
derivative of the so-called azoxystilbene. Its sulphonic acids
dye cotton directly from an acid bath.

This yellow dyestuff is obtained by heating paranitrotoluene-
orthosulphonic acid with alkalies. It yields diamidostilbenesul-
phonic acid on reduction, but whether it is azoxystilbene or
whether a ring-formation between the methane-group and the
azo-chainhas taken place is doubtful [78, 79].

The compound in question is known as Sun- Yellow.

TMotoluidines (Primuline) [80, 81].

By action of sulphur on paratoluidine, Merz and Weith obtained
a base called thiotoluidine (C6H3CIl3NH2).S, M.P. 103". This
reaction takes place at 140° ; and if a higher proportion of sulphur
and a more elevated temperature be employed, two new thiobases
are formed, one of which is known as dehydrothiotoluidine

76 CHEMISTRY OF ORGANIC DYESTUFFS.

C14H12N3S, and the other is the mother-substance of primuline.
The salts of the sulphonic acid of the latter come into commerce as
Primuline, Polychromine, &c. Primuline dyes unmordunted cotton
directly from an alkaline bath, but its principal application is in
connection with the so-called developers. This depends on the
fact that primuline contains an amido-group capable of being dia-
zotised on the fibre. This was introduced technically by Green as
a method of producing insoluble azo-dyes direct on the fibre, the
goods dyed with primuline being diazotised in a slightly acid bath
with sodium nitrite, and then passed into the various yellow, red,
&c. developers, which consist of certain amiues and phenols in
suitable solvents.

Erica.

Metaxylidine gives similar compounds if treated with sulphur.
One of these, M.P. 107°, possesses one amido-group capable of
being diazotised, and certain of the azo-dyes prepared with it form
the various brands of Erica. These dyestuflfs have the remark-
able property of dyeing cotton from a bath containing sulphate of
soda, producing pleasing pink shades of considerable fastness.

Erica B is the result of the combination of dehydrothiometa-
xylidine with a-naphthol-e-disulphonic acid.

Thioflavine.

The Thioflavines, although not azo-dyes, are closely related to
Primuline, and may therefore he described here.

By action of methyl chloride on dehydrothiotoluidine from the
primuline melt, two compounds are formed, one of which comes
into commerce in the form of its hydrochloride as Thioflavine T.
It is a basic dyestuff", producing fine greenish shades of yellow.
The second product of the reaction, which is separated from the
previous one by means of its sparing solubility in dilute hydrochloric
acid, yields on treatment with fuming sulphuric acid a sulphonic
acid, a salt of which is sold under the name of Thioflavine S. It
is a substantive dyestuff" applied to cotton from an alkaline bath.

Thioflavine T is a dimethyldehydrothiotoluidine-methyl chloride
of the formula —

AZO-COMP(JUNDS. 77

CH3 CI

CH3-C6H3< ^C-CeH^— N(CH3)2HC1 ;

and Thioflavine S is a sodium salt of dimethyldehydrothiotolui-
diiiesulphonic acid, Ci6Hi5N2S203iSra.

Direct Production' of Azo-uyes on the Fibre.

Azo-dyes prepared by interaction of a diazo-compound and a
phenol are insoluble in water, and therefore of no practical value.
For this reason a sulpho-group is introduced (see p. 34), and this
produces the solubility necessary for their application in ordinary
dyeing processes. These sulphonated azo-dyes have a considerable
affinity for wool and silk, but (with the exception of those of the
tctrazo-series) are not easily fixed on cotton. Cotton may be
dyed with certain azo-dyes of the Crocei'n series, but the shades
produced are not fast to washing.

The ease with which the combination of a diazo-compound and
a phenol takes place, and the purity of the resulting product,
doubtless led to the idea that insoluble azo-dyes might be pro-
duced by direct precipitation on vegetable fibres.

Messrs. Holliday were the first to make a practical application
of the diazo-reaction in this direction, and in 1880 they patented
processes whereby azo-dyes might be produced on vegetable fibres.
Three alternative methods are prescribed : —

I. The goods are impregnated with an alkaline solution of a
phenol, and the colour produced by passage through a solu-
tion of a diazo-compound.
II. The above process is reversed, the diazo-solution being

applied first.
III. The goods are impregnated with a mixture of diazo-compound
and phenol, and the colour developed by passage through
alkali.

Grassier, in the same year, brought out a process whereby the
use of acid to develop the nitrous acid necessary for diazotisation

78 CHEMISTRY OF ORGANIC DYESTUFFS.

is avoided. A mixture of an amine, sodium nitrite, ammonium
chloride, and a phenol is thickened, and the goods impregnated or
printed with the mixture, and the colour developed by drying and
steaming. A shade closely approaching Turkey red is obtained by
using a mixture of xylidine and yS-naphthol.

A process which has been used for silk-dyeing is similar to that of
Messrs. Holliday. A diazo-compound in solution is neutralised by
chalk, and a phenol (yS-naphthol) obtained in a fine state of division
by precipitation is added. On working the goods in this mixture,
the colour is gradually developed and is fixed on the fibre.

Messrs. Meister, Lucius, and Briining have recently modified
the Holliday process, and adopt a method somewhat resembling
the last described. It was found that the presence of free mineral
acid in the solution of the diazo-compound is disadvantageous, and
that brighter and more even shades are obtained if the free acid is
neutralised by addition of chalk, or replaced by acetic acid, this
being effected by addition of sodium acetate. The goods are
worked, first in the phenol dissolved in water in presence of two
molecules of caustic soda, dried, passed into the prepared solution
of the diazo-compound, and washed till the wash-waters are
colourless.

In general the theoretical proportions indicated by equation are
adhered to in the preparation of the diazo-solutions ; certain bases,
however, are not easily soluble, and are brought into commerce
in pastes containing 25 per cent, of amine and the amount of
nitrite necessary for diazotising. The diazo-solution is obtained
by solution in the calculated amount of dilute hydrochloric acid.
The red shades obtained by this process become duller on soaping,
with the exception of those from the amidoazo-compounds. The
shades obtained from amidoazo-compounds are also faster to
light than those from simple amines. The shades obtained with
/3-naplitliol are bright orange-yellow to red, those from a-naphthol
having a brown tone. A shade approximating to Turkey red is
obtained from /3-naphthol and diazotised /S-naphthylamine.

The above processes are purely mechanical, the goods being
simply impregnated with the diazo-compound, or phenol. Another
group of methods differs in an important respect — that the amine
is first actually fixed, by dyeing, on the fibre. It has already been
mentioned that primuline (an amine) may be fixed on cotton.

AZO-COMPOUNDS. 79

diazotised on the fibre, and new azo-colours produced by passage
of the goods through developers, i. e. solutions of amines or
phenols capable of combining with the diazo-compound of primu-
line. It is evident that this method must be more advantageous
than those in which the diazo-compound is in mere mechanical
incorporation with the fibre, shades produced by the latter process
being more liable to rub.

Of late a new class of direct-dyeing cotton-colours has been
introduced. These contain one or more free amido-groups capable
of diazotisatioUj and are therefore suitable for direct production of
azo-dyes on the fibre. Amongst these dyestufifs are Diamine Blue-
Black E, Diamine Black B and E. (see Table). These dyestuff*s
are combinations of diazotised bases of the Benzidine series with
one or two molecules of an amidonaphtholsulphonic acid, and
these amido-groups, in the naphthol compound remaining intact,
may subsequently be diazotised.

Cotton is dyed in a bath containing Glauber's salt and a little
soap or soda, and the shades produced vary from dark blue to
bluish black, about 6 per cent, of dyestuff being necessary to pro-
duce a maximum efffect. The dia^otising is effected by a bath of
sodium nitrite acidified with hydrochloric acid. The developing-
bath varies according to the shade required. Resorcin,/3-naphthol,
and phenylenediamine produce blacks of various shades ; blues are
obtained with naplithylamine ether; and mixtures of these deve-
lopers produce blacks of every conceivable shade.

In all these processes depending on the use of diazo-compounds
the principal point is to work as cold as possible. Diazo-com-
pounds decompose with a slight elevation of temperature, and are
unstable at ordinary temperatures, and therefore it is necessary to
work as expeditiously as possible. In the Holliday and allied pro-
cesses, where a diazo-compound is used in solution, ice is frequently
necessary for its preservation ; where the diazo-compound is pro-
duced on the fibre, this is not of such great moment.

80 CHEMISTRY OF ORGANIC DYESTUFFS.

CHAPTER III.

OXYQUINONES AND QUINONEOXIMES.

The quinones belong to the most powerful class o£ cliromogens, and
this is equally true of both the para- and orthoquinones. They
yield actual dyestuffs by introduction of auxochromic groups. The
oxyquinones possess a specially marked dyestufF-character, as the
quinone group belongs to the acid-forming chromophors, and the
hydroxyl group introduced develops powerful acid properties.

All the oxyquinones are coloured and form salts of still darker
colour. Most of them may be fixed directly on animal fibres, but
the shades obtained are weak and without value.

The true character of a number of these bodies only appears in
their combinations with metallic oxides ; in other words, the oxy-
quinones belong to the class of " mordant-dyeing " colouring-
matters. They are especially distinguished by the beauty and
fastness of their metallic lakes.

An interesting property in connection with these bodies is
that only such oxyquinones as have one hydroxyl group in the
ortho-position to the quinone-oxygen possess this power of dyeing
on mordants, and that in general it is necessary to have simul-
taneously two hydroxyl-groups in the ortho-position to each other
[32, 33].

The rest of the oxyquinones form coloured metallic salts which
are often insoluble, but which do not possess the essential pro-
perty of adhering to fibre.

The oxyquinones of the benzene series contain at least one
hydroxyl group besides the quinone-oxygen, and so far as they
have been examined are capable of dyeing on mordants in a greater
or less degree. Tetroxy quinones, rhodizonic acid (dioxydiquinoyl)
and nitranilic acid (dinitrodioxyquinone) have great power in this

OXYQUINONES AND QUINONEOXIMES. 81

direction, while it is present to only a slight extent in dioxyquinone
and chlor- and bromanilic acids.

The tinctorial power of these bodies is, however, slight, and a
dyestuff of sufficient intensity and stability is only reached in the
naphthalene series. This is naphthazarin, a dioxyquinone of un-
known constitution.

The quinoneoxiraes closely resemble the oxyquinones in their
properties. Only compounds derived from orthoquinones are
capable of fixation on mordants. Mono- or dioximes are formed
by substitution of one or both quinone-oxygen atoms in an ortho-
quinone by the isonitroso-group NOH.

Both may be dyed on metallic mordants, especially on iron or
cobalt oxide. The mono-oximes, however, are more useful in this
respect, and have for some time been applied technically.

Najphthazarin ( Dioxynajylitlioqiiinone).
CioHA(OH)2.

This compound was discovered by Roussin in the year 1861,
and for some time was thought to be'alizarin. It is obtained by
heating a-dinitronaphthalene with concentrated sulphuric acid,
fragments of zinc being added to the hot solution. It sublimes in
brown needles, with a cantharides lustre. It is sparingly soluble
in water, easily in alcohol and glacial acetic acid, with a red colour.
It forms a blue solution with alkalies and a red one with strong
sulphuric acid. It combines with sodium bisulphite, and the com-
pound formed dissolves readily in water. Naphthazarin dyes
excellently on mordanted fibres, giving a violet on alumina and
a grey on chromic oxide.

Naphthazarin has recently been introduced into commerce as
Alizarin Black. The commercial product is the bisulphite com-
pound, and finds its principal application in printing. For this
purpose it is mixed with chromium acetate. On steaming the
bisulphite compound is decomposed, and the naphthazarin com-
bines with the chromic oxide to form a firmly adhering lake.

Antiiraquixone Dyestuffs.

Anthraquinone itself has only a slight yellow colour, while all
its hydroxyl derivatives have a more or less marked colour, gene-
rally orange-yellow to red. The solutions of the alkali-salts are

82 CHEMISTRY OF ORGANIC DYESTUFFS.

generally red or violet. Certain of these bodies possess affinity for
animal fibres, and may be fixed like acid colours, but the shades
produced have no practical value.

The utility of these dyestufl's depends solely on their capability
of forming insoluble lakes with metallic oxides. These lakes may
be firmly fixed on textile fibres, their colour varying according to
the nature of the metal. Indeed the metallic compounds of these
bodies may be looked upon as so many diff'erent dyestufl's.

Of the numerous hydroxyl derivatives of anthraquinone, only
those which have two hydroxyl-groups in the 1, '3-position to the
carbonyl-group of anthraquinone are capable of dyeing upon
mordants. In other words, only alizarin and its derivatives possess
this property. As the number of anthraquinone derivatives is very
large, we must necessarily confine ourselves to those of technical
value.

Alizarin [2, 3].
C14H8O4.

Alizarin is one of the few natural dyestuffs which have been
prepared synthetically, and is probably the only one which is pre-
pared artificially on the large scale. It occurs generally as a
glucoside, ruberythric acid C26H28O14 [1, 2] in madder, the root
of Rubia tinctorium, and also in some other plants.

Ruberythric acid splits up by boiling with dilute acid, or by
fermentation, glucose and alizarin being formed.

C26H28O14 + 2H2O = C14H8O4 + 2C6H i20e.

Alizarin crystallises in reddish-brown needles, which are almost
insoluble in water, sparingly soluble in alcohol, more easily in hot
glacial acetic acid, carbon disulphide, and glycerine. It melts at
289° to 290° C, and sublimes at a higher temperature in beautiful
long red needles. It dissolves in alkalies with a violet colour, and
the sparingly soluble acid salts may be precipitated from these solu-
tions by carbonic acid. On oxidation with nitric acid it gives
phthalic acid, and by heating with zinc powder anthracene is
formed. With the oxides of aluminium, barium, calcium, iron, and
most of the heavy metals it gives characteristic coloured insoluble
lakes. The red alumina lake, the maroon chromium lake, and the
violet- black iron lake are of importance in dyeing.

The hydroxyl-groups in alizarin are in the adjacent positions

OXYQUINONES AXD QUINONEOXIMES.

to one carbonyl-group of anthraquinone, and its constitution may
be expressed by the following formula [4] : —

CO OH

The hydroxyl-hydrogeu atoms of alizarin may be replaced by
alcohol and acid radicals. The alkyl derivatives are easily obtained
by heating alizarin with the requisite alkyl iodide in presence of
caustic alkali. Mono- and di-derivatives may be obtained in this
manner [5, 6].

Acetic anhydride gives a diacetyl derivative,, M.P. 160° C. [7].
Chlorine acts on alizarin, forming a monochloralizarin ; with
antimony pentachloride, dichlor- [8] and finally tetrachlor-alizarin
maybe obtained. Corresponding bromine derivatives have also
been prepared [8, 9, 10]. '•

On heating with ammonia in sealed tubes two isomeric ali-
zarin amides (oxyamido-anthraquinones, Ci4H602(OH)NH2) are
obtained. The principal product of the reaction is the meta-com-
pound with a small quantity of the ortho.

Sulphonic acids of alizarin have also been prepared, and are
met with in commerce under the name of Alizarin Ked S.

Alizarin may be prepared artificially by fusing dibromanthra-
quinone, nitroanthraquinone, or anthraquinonesulphonic acid with
potash or soda [3] ; also by condensation of phthalic acid with
pyrocatechin [4], and by reduction of rufigallic acid [13]. Ali-
zarin has only been prepared on an industrial scale from anthra-
quinone, and the artificial product has practically displaced madder
in the course of the last twenty years.

The synthesis of alizarin was first eff'ected by Graebe and
Liebcrmann in 1869. These chemists had already observed the
formation of anthracene from natural alizarin by heating with
zinc powder, and recognizing alizarin as a derivative of anthra-
cene, attempted to convert anthracene into alizarin. This aim
was accomplished by fusion of bibromanthraquinone with potash.
In the same year Graebe, Liebermann, and Caro [14] discovered
the formation of alizarin by melting anthraquinonesulphonic

84 CHEMISTKY OF ORGANIC DYESTUFFS.

acid with caustic potash. This process, which is in use at the
present day, was discovered ahuost simultaneously by W. H.
Perkin [15].

Other processes have been proposed for the manufacture of
alizarin, for instance by melting dichloranthraquinone or nitro-
anthraquinone [16] with caustic potash, but these processes have
never attained commercial importance.

For a long time it was thought that the anthraquinonedisul-
phonic acids gave rise to the formation of alizarin, but this
assumption was based on an error. The monosulphonic acid alone
is capable of giving alizarin, while the disulphonic acids yield
isopurpurin and flavopurpurin. This was already known to some
technologists in 1871, but was first published by Perkin in 187G

[17].

The formation of alizarin from anthraquinonesulphonic acid
does not appear to be due to any uniform reaction. On the one
hand, oxyanthraquinone is formed and becomes oxidised in the
alkaline melt to alizarin ; on the other hand, oxyanthraqui-
nonesulphonic acid is also a constituent of the melt, and yields
alizarin by replacement of its sulpho-group by hydroxyl. Aliza-
rinsulphonic acids are also often found in the alizarin melt. It
is not improbable that these different reactions are due to the
existence of several isomeric anthraquinonesulphonic acids.

For the manufacture of alizarin on a large scale a very pure
anthraquinone is required, and this is generally prepared by oxi-
dation of anthracene with sodium bichromate and dilute sulphuric
acid. The anthracene is generally a 50-per-cent. product which
has oeen converted into a soft powder by subliming with super-
heated steam. The oxidation takes place in lead-lined vessels in
which the mixture is heated by direct steam. By employing a
pure anthracene and a not too concentrated oxidation-mixture, the
anthraquinone separates as soft grey powder, which is freed from
acid by washing with water. The crude product is then dried,
dissolved in concentrated sulphuric acid, and precipitated with
water. A further purification is efiected by sublimation with
superheated steam.

For production of monosulphonic acid a somewhat concentrated
fuming sulphuric acid (containing 30 to 40 per cent, anhydride)
is required, and the sulphonation should take place at as low a
temperature as possible.

OXYQUINONES AND QUINONEOXIMES. 85

The monosulplionic acid is separated from the disulphonic acids
simultaneously formed by fractional crystallisation of the sodium
salts. By saturating the acid mixture with soda, the salt of the
monosulphonic acid separates first. At present the sulphonation
is carried out so as to produce as much monosulphonic acid as
l)ossible with only a little disulphonic acid.

As lias already been stated, the reaction in the melt proceeds in
two directions, viz., a substitution of the sulpho-group by hydroxyl
and a direct oxidation.

In the older processes this oxidation was efiiected by air, and if
the supply of this was insufficient, took place at the cost of some of
the materials. To prevent this a large surface of the melt was
exposed to the air by melting in shallow pans.

This process has been abandoned for about ten years, and the
atmospheric oxygen is dispensed with by adding an oxidising agent
(potassium chlorate), and operating in closed vessels under pres-
sure. This improvement is of great advantage, as the temperature
is easily regulated, even if the melt contains much water ; while in
open vessels a certain concentration is necessary before the required
temperature is reached. In place of the older melting process,
the sulphonic acids are now heated with concentrated soda-lye
under pressure.

The operation takes place in a horizontal cylindrical iron vessel
fitted with a stirrer. Into this are introduced one part of anthra-
quinonemonosulphonate of soda, with about three parts of caustic
soda and a certain amount of water and chlorate of potash. The
mixture is then heated several days to 180^-200°.

The melt is then dissolved in water and the sodium compound
decomposed by adding hydrochloric acid. The precipitate of
alizarin is then well washed, and brought into commerce as a
10 to 20 per cent, paste. Its value may be ascertained by an esti-
mation of the solid matter and ash, a dye-trial also being made.

Blue and yellow shades of alizarin are known ; the former con-
sists of pretty pure alizarin, while the latter contain both the
trioxyanthraquinoncs isopurpurin and flavopurpurin. Alizarin
may be fixed directly on wool, the shade produced being weak, and
of the yellowish-red tone characteristic of free alizarin solutions.
This shade has no value in dyeing, and the application of alizarin
is solely in form of its brightly coloured aluminium, chromium, and
iron lakes.

86 CHEMISTRY OF ORGANIC DYESTUFFS.

Most of the alizarin made is used in cotton-dyeing and printing^
although a considerable amount is also used in wool- dyeing.

Alizarin gives entirely different shades with different metals.
In dyeing and printing the beautiful red alumina lake and the
violet-black iron lake are almost exclusively used. Sometimes the
chromium lake is also applied.

In order to dye alizarin on cotton, the latter is impregnated
with the necessary metallic oxide, and brought into a bath con-
taining alizarin in a fine state of suspension, the bath being gra-
dually heated to boiling; although alizarin is so slightly soluble
in water, its solubility is sufficient to effect its combination with
the metallic oxide on the fibre. For test-dyeing with alizarins
printed calico is used. This calico contains stripes of alumina and
iron and mixtures of these, printed in different degrees of strength,
and on dyeing in an alizarin-bath various shades are obtained.

In printing, a mixture of alizarin paste and aluminium or iron
acetate is used. On steaming, the acetate is decomposed, and the
formation of the colour-lake takes place.

In alizarin-dyeing, a great number of purely empirical opera-
tions are common, especially in turkey-red dyeing. Brilliant
scarlet tones of turkey-red can only be obtained on alumina and
oil mordants. The oil formerly used was a very rancid olive-oil,
" Huile tournante," but this has been entirely replaced by the
so-called turkey-red oil. This product is a ricinoleate of ammonia,
obtained by treating castor-oil with strong sulphuric acid^ and
neutralizing the separated fatty acid with ammonia. It is probable
that the alumina forms double compounds with the fatty acids and
with the alizarin, these compounds possessing a more brilliant
colour than the simple alizarin lakes. The turkey-red process is
very complicated, and comprises many operations which are not
properly understood. For instance, treatment in a bath of cow-
dung and other similar processes.

"Wool is mordanted with alumina, for alizarin-dyeing, generally
by boiling in a bath of alum tartar. Chromium mordants are
also used in connection with alizarin for production of maroon
shades.

The shades obtained with alizarin are very stable. They resist
the action of soap and bleaching-powder, and are almost entirely
unaffected by light.

OXYQUINONES AND QUINONEOXIMES. 87

Nitroalizarin [18, 19].
Ci,H,(N02)04.

(1) (2) (3)

Only the )8-nitro-compound (of the constitution OH OH NO2)
possesses technical interest. It may be obtained by treating
alizarin, suspended in toluene or nitrobenzene, with nitrous acid,
or by cautious nitration of alizarin dissolved in glacial acetic acid
with nitric acid.

Pure y8-nitroalizarin forms orange-yellow needles, which melt
at 244°, with partial decomposition [19]. It sublimes in yellow
leaflets, undergoing partial decomposition. It dissolves in benzene
and glacial acetic acid, and gives a purple-red solution with
alkalies. The violet lime-lake is not decomposed by carbonic
acid. (Distinction from alizarin.) It forms a diacetyl compound,
M.P. 218° [19]. Nitroalizarin dyes orange shades on alumina
mordants, and reddish-violet on iron mordants.

It comes into commerce in paste as Alizarin Orange, and is
used in dyeing and printing, though its principal application is in
the manufacture of Alizarin Blue.

Trioxyanthraquinones.
CuH,(OH)302.
A. Purpurin [position 1, 2, 4].
Purpurin occurs with alizarin in the madder root [20], pro-
bably also as glucoside. It may be obtained artificially from
alizarin by heating with manganese dioxide and sulphuric acid
[21], or arsenic acid; and also by melting an alizarinsulphonic
acid (the so-called alizarin purpursulphonic acid) with potash

[11]-
Purpurin forms long orange-yellow needles which contain one

molecule of water. It dissolves pretty readily in alcohol, ether,

and benzene, and is also much more easily soluble in water than

alizarin. It loses its water of crystallisation at 100°, and sublimes

at a comparatively low temperature. M.P. 253°.

The alkaline solutions of purpurin are reddish violet, and

rapidly become bleached on exposure to light and air. The

presence of certain metallic oxides produces a characteristic effect

on the absorption-spectrum of purpurin solutions, and these may

88 CHEMISTRY OF ORGANIC DYESTUFFS.

serve for the detection of alumina and magnesia [22, 23] . Pur-
purin dissolves in boiling alum solution, forming a yellowish- red
fluorescent solution, from which the purpurin separates on cooling.
As alizarin is almost insoluble in alum solution, this method is
used for the separation of these bodies. Although the alkaline
solutions of purpurin are easily bleached by light, the alumina
lake is perfectly stable against this agency.

On alumina mordants purpurin produces a beautiful scarlet
red, much yellower in tone than that from alizarin, but its appli-
cation is limited, as its price is much higher than that of iso-
purpurin.

B. Isopurpurin {Anthrapurpurin) [24, 25, 26].
OH[5]C.H3{mC«[J]}c.H.([«]OH

Isopurpurin is obtained by melting /3-anthraquinonedisul phonic
acid with caustic potash, an isomer of alizarin, isoanthraflavic
acid, being formed as a bye-product [26] .

In the first stage mono-oxyanthraquinonesulphonic acids,

are formed, and these are oxidised to alizarinsulphonic acids, a
small portion being converted into anthraflavic acids. These aliza-
rinsulphonic acids yield the purpurins by exchange of a sulpho-
for an hydroxyl group [42] .

It forms orange needles, which are soluble in alcohol but in-
soluble in benzene. Its M.P. is above 330° [25]. It yields no
phthalic acid on oxidation, and therefore probably contains the
third OH-group in the second benzene ring. Isopurpurin is the
principal constituent of the commercial alizarin for red. It dyes
a fine scarlet red on alumina ; its iron lake is greyish violet, and of
little value.

C. Flavopurpiirin [26, 27].
0HMC.H3{W,C0P]}c.H.{[«]g

OH
H'

Kavopurpurin is obtained from a-anthraquinonedisulphonic
acid ; anthraflavic acid, an isomer of alizarin, is formed as a bye-

OXYQUINONES AND QUINONEOXIMES.

product. It forms golden-yellow needles, easily soluble in alcohol,
M.P. above 330° C, It dissolves with purple-red colour in caustic
soda, and yellowish-red in ammonia and sodium carbonate.

On alumina mordants it gives a red, which is still yellower than
that with isopurpurin. Its principal application is in printing,
while that of isopurpurin is in dyeing. Anthraflavie acid and
isoanthraflavic acid sometimes occur in the commercial products.
They are entirely valueless in dyeing, and are produced in badly
conducted operations.

Like isopurpurin, flavopurpurin contains the third hydroxyl-
group in the secoud benzene nucleus.

D. Anthragallol [41].

This trioxyanthraquinone is not prepared from anthracene, but
is obtained by condensation of gallic acid with benzoic acid. In
anthragallol the three hydroxyl- groups occupy adjacent positions
[1:2:3].

It is prepared by heating equal molecules of benzoic acid and
gallic acid with concentrated sulphuric acid. The following
equation expresses the reaction which takes place : —

Ti on CO OH

OH H

H no

CO
-|-2H,0

Anthragallol has a brown colour, and dyes brown shades on
alumina or chromic oxide. The commercial Alizarin Brown is a
mixture of anthragallol with more or less rufigallic acid.

The latter compound is hexaoxyanthraquinone, and is formed
in a similar manner to anthragallol by condensation of gallic acid.
It belongs to the mordant anthraquinone-derivatives.

Alizarin Bordeaux and Alizarin Cyanine [38, 39].

On treating dry alizarin with a large quantity of sulphuric acid
containing 70 per cent, anhydride, a peculiar ether of sulphuric acid
is obtained, which on boiling with water splits up into a new

CHEMISTRY OF ORGANIC DYESTUFFS.

dyestuff, " Alizarin Bordeaux/' and sulphuric acid. This alizarin
Bordeaux is a tetraoxyanthraquinone identical with quinalizarin :
on CO OH

OH CO

This dyestuff produces fine Bordeaux shades on alumina mor-
dantSj and in colour-printing a blackish blue is obtained with a
chromium mordant. On wool a deep claret with a violet tone may
be obtained. Alizarin Bordeaux crystallises from nitrobenzene
in fine red needles which have a metallic lustre. It may be dis-
tilled, undergoing only slight decomposition.

If alizarin Bordeaux be dissolved in concentrated sulphuric acid
and treated with manganese peroxide or arsenic acid, oxidation
takes place, a pentoxyanthraquinone being formed : —
OH CO OH

OH CO OH
This body comes into commerce as Alizarin Cyanine R or as
Alizarin Blue CR. Alizarin cyanine crystallises from glacial
acetic acid in beautiful crystals, and dissolves in concentrated
sulphuric acid with a blue colour and a fine red fluorescence. If
dyed on cotton mordants with alumina, fine violet shades are
produced, and chromium mordants give dark blues. In the pre-
paration of alizarin cyanine R, a sulphuric ether is formed as
intermediate product, and on treating with ammonia this body
yields a dyestuff which differs from alizarin cyanine R inasmuch as
it produces considerably greener shades. It is also a commercial
product, and is sold under the name Alizarin Cyanine Gr.
Analogous series of reactions may be carried out with the isomers
and homologues of alizarin, for example, '' Bordeaux^'' and " Cya-
nines " corresponding to those described above may be obtained
from purpurin, anthrapurpurin, fiavopurpurin, and anthragallol.

OXYQUINONES AND QUIN0NE0XIME8. 91

Alizarin Blue [28, 29, 30].

This dyestuff is prepared by heating /S-nitroalizarin with
glycerine and sulphuric acid. It is peculiar in so far that it
possesses the lake-forming properties characteristic of the alizarin
dyes, and is at the same time a weak base. Alizarin blue was
discovered by Prud^homme [28], and the determination of its
constitution by Graebe [29] led to the synthesis of quinoline by
Skraup from glycerine, nitrobenzene, and aniline.

Alizarin blue has the composition C17H9NO4, and stands in
the same relation to alizarin as quinoline to benzene.

Its constitutional formula is as follows [29] : —

CO OH

In the pure state (crystallised from benzene) it forms brownish-
violet needles, insoluble in water and difficultly soluble in ether
and alcohol. It melts at 270°, and sublimes, forming orange
vapours. It dissolves in alkalies with a blue colour, an excess of
alkali turning the solution green. Its salts with acids are of a
reddish colour, and are decomposed by water.

On distillation with zinc powder it yields anthraquinoline,
Ci;HnN [29].

With chromium oxide, alizarin blue gives a stable indigo-blue
lake.

It is chiefly applied in the form of its bisulphite compound, the
latter being the principal constituent of the commercial Alizarin
Blue S [31]. This is a reddish-brown compound and is decom-
posed on heating, alizarin blue separating. The bisulphitf^ com-
pound is printed with acetate of chromium ; and, on steaming, the
chromium lake of alizarin blue is fixed on the fibre. The bisul-
phite compound may be precipitated from its solutions by common
salt, and comes into commerce as an easily soluble brown powder.

92 CHEMISTRY OF ORGANIC DYESTUFFS.

Alizarin Indigo-hlue S, Alizarin Green S [40].

Alizarine blue may be oxidised by action of fuming sulphuric
acid, the process being analogous to that used for the preparation
of Alizarin Bordeaux. At 50° to 60° a dyestufF called Alizarin
Blue-green is formed, and is best isolated in form of its bisulphite
compound. It is a monosul phonic acid of mono-oxy alizarin blue.

If the mixture be heated to 120°, or if alizarin blue-green is
heated with concentrated sulphuric acid to 120°, an intramolecular
change takes place, a new mono-oxyalizarin blue monosulphonic
acid being formed. This body is an article of commerce, and is
known as Alizarin Green S.

If, finally, the temperature of the reaction between sulphuric
acid and alizarin blue be raised to 200° to 210°, or if alizarin
green is heated to the same temperature with concentrated sul-
phuric acid, a third dyestuff. Alizarin Indigo-blue, is obtained.
This body is a trioxyalizarin-blue. The commercial products are
pastes which contain the bisulphite compounds. The shades pro-
duced in dyeing are sufficiently indicated by the names, being a
dull indigo-blue and a dull bluish green respectively. The best
results are obtained with chromium mordants.

Stijrogallol [36, 37].
CieHgOg.

This compound is obtained by heating gallic acid with cinnamic
acid in sulphuric acid solution to 55°. It forms light yellow
needles. M.P. 350°. It is insoluble in water, and sparingly
soluble in alcohol, glacial acetic acid, and aniline.

Its solution in alkalies is green, changing through violet to red
on warming. It dissolves in strong sulphuric acid with a yellowish-
red colour.

Styrogallol is probably an o-dioxyanthracoumarine. On warming
with acetic anhydride a diacetyl derivative, M.P. 260°, is obtained.

On alumina mordants it dyes an orange-yellow shade, similar
to alizarin orange, but owing to its high price has not been used
practically.

A dibrominated dioxy-yS-methylcoumarine is known commer-
cially as Anthracene Yellow.

OXYQUINONES AND QUINONEOXIMES.

QuiNONEOXIMES.

These compounds are obtained by action of nitrous acid on
phenols, and were formerly regarded as nitrosophenols ; but this
assumption has gradually been abandoned. They may also be
obtained by action of hydroxylamine on quinones, and yield
dioximes on further treatment with this reagent. It is therefore
more probable that the nitrosophenols are really oximes of quinones,
i. e., quinones in which one oxygen atom is replaced by the divalent
group = N — OH.

0 NOH

Quinone.

Quinoneoxime
(Nitrosoplxenol).

The quinoneoximes, like the quinones, are mostly yellow, but
possess little tinctorial power. Certain oxime-derivatives of ortho-
quinones, however, like oxy quinones, are capable of combining
with mordants (especially iron and cobalt), forming highly coloured
lakes which may be fixed on textile fibres.

Some of this latter class of quinoneoximes are described in
detail, as they have attained some importance as adjective dye-
stuffs.

Dinitrosoresorcin (Biquinoyldioxime) [32].
CeHACNOH)^.

This compound is obtained by treating an aqueous solution of
resorcin with nitrous acid (sodium nitrite and sulphuric acid).
Dinitrosoresorcin crystallises from alcohol in yellowish-brown
leaflets, which deflagrate at 115°. It is a pretty strong dibasic
acid, and forms easily soluble salts with alkalies.

Its constitution is probably expressed by the following formula
[33] :-

CHEMISTRY OF ORGANIC DYESTUFFS.
O

NOIi

Is" Oil

The iron lake of dinitrosoresorcin is green^ and the latter
produces green shades on cotton prepared with iron mordants. It
has been used for some time in cotton-dyeing under the name
" Fast Green/'

Naphthaquinoneoximes [34].

CioH60(NOH).

/3-naphthaquinone yields two oximes^ both of which are capable
of dyeing on mordants, while this property is absent in the oxime
of a -naphtha quinone (a-nitroso-a-naphthol),

NOII

a-nitroso-/3-naphthol is obtained by action of nitrous acid on
j8-naphthol, while a-naphthol under similar treatment gives
yS-nitroso-a-naphthol,

^NOH

along with some a-a-compound.

Both derivatives of /3-naphthaquinone give intensely green lakes
with ferric oxide, while their cobalt lake is dark red, being known

OXYQUINONES AND QUINONEOXIMES. 95

in commerce as Gambine R and G respectively ; but they are not
of great importance.

The iron salt of a sulphonic acid of the a-/3-componnd comes
into commerce as Naphthol Green [38, 39].

The sulphonic acid is prepared by acting on Schaeffer's acid
with nitrous acid. Tlie iron compound of this acid is soluble in
water, and is fixed on animal fibres like the acid dyestuflfs.

Naphthol green is used to some extent in wool-dyeing.

The dyestuff known as Dioxiue is a nitroso-derivative of 18
dioxy naphthalene.

96 CHEMISTRY OF ORGANIC DYESTUFFS.

CHAPTER IV.

KETONEIMIDES AND HYDRAZIDES.

These bodies, certain of which have been used as dyestuffs, are
derived from the simple ketones in the same manner as the quinone-
imides and quinone-hydrazides from the diketones (quinones).
Here, however, the chromophor occurs in an open carbon chain,
and as it is only of a weak character, requires a salt-forming
group to develop the properties of a dyestufP. The colour produced
is always yellow.

It has already been remarked that the CO group, when it does
not occur as a member of a closed carbon ring, cannot act as a
chromophor, and only becomes one when the oxygen is replaced
by sulphur or by a nitrogenous group. So far as the present
state of knowledge reaches, all benzophenone derivatives are
colourless. On the other hand, thiobenzophenone yields coloured
derivatives. Tetramethyldiamidothiobenzophenone [3] : —

(CH3)2NC6H^^g

(CH3)2NC6H/ '

for example, is intensely yellowish red, but is no dyestuff.

If the sulphur in this compound be replaced by the imide-group
KH, auramine, the only representative of the ketoneimide dye-
stuffs known, is formed.

The starting-point for the manufacture of auramine is tetra-
methyldiamidobenzophenone,

(CH3)2NCeH^^^

(CH3)2NC6H/

This base was discovered by Michler [2] in 1876, and has

KETONEIMIDES AND IIYDRAZIDES. 97

recently become an important product for tlie manufacture of
triphenylmethane dyestuffs.

Tetrametliyldiamidobenzopiienone is obtained by action of
carbon oxycliloride or of perclilorformic ether on dimethylaniline.

The analogous thioketone already mentioned is obtained in a
similar manner from carbon sulphochloride, CSCI2, and dimethyl-
aniline; it may also be obtained by treating the corresponding
oxygen ketone with phosphorus sulphide. The two ketones are
similar in their reactions [3] .

By action of nascent hydrogen, tetramethyldiamidobenzophe-
none is converted into the corresponding benzhydrol [1]: —

(CH3)2NCeH,^^/OH

(ch3)2Nc,h/ ^h •

This compound combines with acids to form beautiful blue
salts, which, like the dyestuffs of the rosaniline series, are de-
colorised by excess of acid. It is probable that in these coloured
salts the compound exists as an anhydride, as is the case with the
rosaniline salts. The hydrochloride, for instance, has the consti-
tution : —

(CH3)2N-CeH,^

(CH3).N-CeH/9-^-

Cl^l 1

The chloride obtained by treating tetramethyldiaraidobenzo-
phenone with a phosphorus chloride is probably not the simple
chloride

^ '^' " >C=Cl2;

hut, as it possesses a deep blue colour, is constituted according to
the formula : —

(CH3)2N-C6H^

Cl^l ^1

98 CHEMISTRY OF ORGANIC DYESTUFFS.

Auramine [1, 4, 5, 7].

This dyestuff was discovered simultaneously by A. Kern and
H. Caro, and is formed by action of ammonia on tetramctliyl-
diamidobenzophenone. It is best prepared by melting this base
with ammonium chloride and zinc chloride. The reaction is
expressed by the equation : —

C17H20N2O + NH3 = C17H21N3 + H2O.

Another process for the manufacture o£ auramine consists in
allowing ammonia to act on a mixture of tetramethyldiamidodi-
phenylmethane or tetramethyldiamidobenzhydrol with sulphur at
180°.

Auramine is also prepared industrially as follows : —
Dimetliylamidobenzoic chloride is produced by action of phos-
gene on dimethylaniline ;

C6H5N(CH3)o + COCl2=C6H4-N(CH3)2 + HCl.

CO CI

This chloride is treated with diphenylamine, whereby dimethyl-
amidobenzodiphenylamine is formed ;

CeH^-NCCty,

I
CO-N(C«H5)2

Practically, the above reactions are combined into one operation.
The above condensation-product is treated with a chloride of
phosphorus or phosgene, and the resulting chloride,

CeH,-N(CH3)2

I
C-Cl2.N(CeH,)2

condensed with dimethylaniline, and the compound produced

CeH^.NCCHs)^
C^N(C6U,)2

\C6H4.N(CH3)2.C1

heated with ammonia yields auramine and diphenylamincr

KETONEIMIDES AND HYDRAZIDES. 99

Auramine comes into commerce as the hydrochloride C17H21N3,
HCl. This salt is easily soluble in water, and crystallises from
this medium in beautiful golden-yellow leaflets.

It is decomposed by continued boiling with water, especially
in presence of free hydrochloric acid, tetramethyldiamidobenzo-
phenone and ammonia being regenerated.

Platinum double salt, (Ci7lI.2in3,HCl)2,PtCl4, forms an orange-
red precipitate.

Picrate, Ci7H2iN3,CyH2(N02)30H, forms yellow leaflets sparingly
soluble.

Oxalate, (Ci7H2iN3)2C2H204, forms yellow needles sparingly
soluble in water.

Leuco-auramine [7], C17H23N3, is formed by reduction of an
alcoholic solution of auramine with sodium amalgam. It forms
colourless crystals, M.P. 135°, and dissolves in glacial acetic acid
with a blue colour (see under) .

Phenylauramine and tolylauramine are obtained by action of
aniline and toluidine on auramine or on tetramethyldiamido-
benzophenone. ..

Auramine must be regarded as the imide of tetramethyldiamido-
benzophenone, and accordingly has the constitutional formula : —

(CH3)2N— CfiH^x

(CH3)2N-CeH,

The ring constitution accepted for tetramethyldiamidobenz-
hydrol cannot be present in auramine, as the elements of consti-
tutional water necessary are not present. The yellow colour of
auramine also is against the assumption of a ring formula, the
benzhydrols being blue.

On the other hand, a ring-formation is probably present in the
blue salt formed by leucoauramine and acetic acid, and this Graebe
expresses by the formula : —

Xh4n=(ch3);

An objection to this formula is that till now pentatomic
nitrogen is only known in combination with an acid radical or

100 CHEMISTRY OF ORGANIC DYESTUFFS.

hydroxyl. Auraraine and its derivatives are the only dyestuffs
known which belong to the class of simple ketoneimides. The
chromophor^ C=NH, unlike that in rosaniline dyestuflfs, occurs
in an open chain, and in this respect the hydrazides (Tartrazine)
are similar, and also have a yellow colour. Auramine is one of
the few basic yellow dyestuffs, and owing to its easy fixation on
tannin mordants has obtained a considerable importance in cotton-
dyeing and printing. It produces a pure yellow shade.

Its substitution-derivatives, such as phenylauramine, have
mostly a brown colour, and have not been applied practically.

Phenylhydrazides [8].

Phenylhydrazine reacts readily with most compounds which
contain the group CO ; the oxygen atom being eliminated in the
form of water with two hydrogen atoms of the phenylhydrazine,
the rest of the latter entering in the place of the oxygen.

It is probable that the two hydrogen atoms which split off
belong to the amido-group, and therefore the hydrazides contain
the group C=N— NHCcHs.

That a close relationship exists between azo-compounds and
hydrazides is seen from the fact that certain oxyazo-compounds
obtained from diazo-compounds and phenols are identical with the
hydrazides of certain quinones. Indeed all coloured hydrazides
show a great similarity to the azo-compounds, and probably
belong to this class. Both classes of compounds, for example,
behave similarly on reduction. The hydrazine group, like the
azo-group, is split, yielding two amido-groups, one of which
remains in combination with the phenyl group, the other with
the carbon atom.

All the hydrazides known at present have a yellow or orange
colour, like the simpler azo-compounds.

Tartrazine.

This dyestuff is manufactured by action of phenylhydrazine-
sulphonic acid on dioxy-tartaric acid. This acid, which in the
hydrated condition has a formula

KETONEIMIDES AND HYDRAZIDES. 101

COOH

/OH
\0H

I \0H
COOH,

must be regarded as the hydrate of a diketonic acid :

COOH

I
CO

COOH.

It reacts according to the latter formula with hydrazines, two
molecules of which enter into reaction.

The product obtained with two molecules of phenylhydrazine
has a beautiful yellow colour; it is too sparingly soluble to be
of use in dyeing, but a valuble dyestuff may be obtained by intro-
duction of sulpho-groups.

The commercial product known as Tartrazine is a sulphonic acid
prepared by the action of two molecules of phenylhydrazine-
sulphonic acid (from sulphanilic acid) on one molecule of sodium
dioxy tartrate in hydrochloric acid solution. The constitution of
tartrazine is probably expressed by the following formula : —

COOH

C = N-NHC6H4S03H

I
C=N-NHC6H4S03H

I
COOH.

The sodium salt of tartrazine forms a fine orange-yellow
crystalline powder. It dyes animal fibres from an acid bath,
producing a beautiful gold-yellow shade, which is valuable for
its stability against light and milling.

The application of higher hydrazines gives rise to dyestuffs of
a redder tone.

102 CHEMISTRY OF ORGANIC DYESTUFFS.

CHAPTER V.

TRIPHENYLMETHANE DYESTUFES.

Triphenylm ETHANE aiid its analogues are mother substances
of a series of dyestuffs, many of which are of great technical
importance.

If amido- or hydroxyl-groups are introduced into triphenyl-
methane, in certain positions, colourless compounds, the leuco-
derivatives of dyestuft's, are formed.

For example, if three amido-groups are introduced into the
three benzene nuclei, in the para position to the methane-carbon
atom, the compound known as paraleucanilinc is formed,

HgNCeH-

H^NCeH/ j
H

On oxidation this compound loses two hydrogen atoms, and a
condensation takes place between the nitrogen of an amido-group
and the methane-carbon atom, pararosaniline being formed. [See
Introduction.]

HsNCeH.

H^NCeH/^ I'
NH

Pararosaniline only exists in the form of its salts, and in the
free state takes up one molecule of water, triamidotriphenyl-
carbinol, a colourless compound, being formed.

H^NCeH,^

H.NCgH/

TRIPHENYLMETHANE DYESTUFFS.

103

This transformation into colourless carbinol-derivatives takes
place with all basic triphenylinctliane dyestuffs^ and the carbinols
are for this reason regarded as the bases of the dyestufFs, although
this assumption is not altogether correct. Really both classes of
compounds have totally different constitutions^ as in the dyestufEs
a closed ring is present, Avhilc in the carbinols it is absent. In
the triphenylmethane dyestuffs the chromophor =C — NH — or
iC — O — is always present, and generally effects the linkage
between several aromatic nuclei. In most cases it occurs, how-
ever, in one ring, occupying two para positions. For instance_,
pararosaniline contains the group :

Nil

N— II

■which shows a certain analogy to quinones.

The imido-group present in the chromophor also serves as salt-
forming group, and appears to effect a combination of the dye-
stuff' with the fibre. For instance, animal fibres may be dyed with
the colourless carbinol bases, just as with the dyestuffs them-
selves. Apparently a salt is formed, in which the fibre acts as an
acid, and combines with the imido-group.

The basic properties of the amido-groupss present only be-
come apparent under the influence of strong acids, or of the
haloid derivatives of the alcohol radicals. These amido-groups,
however, intensify the basicity of the imido-group. The forma-
tion of salts with these groups is generally attended by a striking
alteration of the dyestuff character.

Basic triphenylmethane dyestuffs mostly form sulphonic acids ;
these are generally acid dyestuffs, and when observed in the free
state or in form of their acid salts have the same colour as the

104 CHEMISTRY OF ORGANIC DYESTUFFS.

original dyestufFs. Their neutral alkali salts are colourless, and
appear to be carbinol compounds.

The conversion of basic carbinols into dyestufFs is generally
gradual, and in many cases the formation of colourless salts of the
former may be observed. Tetramethyldiamidotriphenylcarbinol
(the base of malachite green) gives a colourless solution with
dilute acetic acid, the formation of dyestuff only taking place on
warming or after long standing.

Numerous methods are employed for the production of tri-
phenylmethane dyestufFs.

Substituted benzophenones may be condensed with tertiary
bases in presence of a dehydrating agent.

(CH3)2NC6H,^^

(CH3)2NC6H/

:C0 + C6H5N(CH3)2 + HC1=

Tetramethyldiamidobenzophenone. Dimethylaniline.

(CH3),NCeH,

(CH3).nc.h/-^««^^(^«^)^^«^^-

"I
CI

Hexamethylrosaniline.

The chloride of tetramethyldiamidobenzophenone reacts in a
similar manner. This compound has a blue colour, and probably
belongs to the diphenylmethane dyestufPs, which are analogous to
the rosanilines. It has the constitution : —

(CH3).NC,H,^^_^j

(CH3)2NCeH/j

Benzhydrol obtained by reduction of tetramethyldiamidobenzo-
phenone (compare page 94), and which also in form of its salts
behaves like a dyestuff, reacts with amines with the greatest ease.

In this reaction the leuco-derivatives of the dyestufFs are
obtained.

TRIPHENYLMETHANE DYESTUFIS. 105

(CTl3)2N . C„H4. /H

0 w +C6H5N(CH3),
Tetramethyldianiidobenzhydrol. Dimethylaniline.

(CH3)2N.C,H/| " ^ ^ ^^2
H
Hexamethylparaleucaniline.

Colouring-matters (rosaniline, methyl violet) of this class are also
formed by oxidation of primary, secondary, or tertiary amines,
which contain methyl groups in combination with nitrogen or
carbon. Further, benzene- derivatives, which contain no methyl
groups, yield dyestufFs if treated with compounds which at the same
time are capable of withdrawing hydrogen and supplying carbon,
such as carbon tetrachloride, oxalic acid, iodoform (rosolic acid,
diphenylamine blue). Another method consists in the direct
introduction of amido-groups into triphenylmethane. Again,
aromatic bases or phenols yield triphenylmethane-derivatives by
condensation with toluenes, chlorinated in the side chain, or with
aromatic aldehydes. In most of these cases leuco-compounds are
obtained, and are converted into dyestuflfs by oxidation. The
phthaleins, a peculiar class of triphenylmethane dyestuffs, are pre-
pared by condensation of phthalic anhydride with phenols.

A. EOSANILINE DYESTUFFS.

In the wider sense of the term, this class comprises all the basic
dyestufFs obtained from triphenylmethane and its homologues.
As has already been remarked, the salts are the real dyestuffs,
while the so-called colour-bases are colourless carbinol derivatives.
Up to the present, no suitable nomenclature has been applied to
the actual dyestuffs, rosaniline for example being generally called
triamidotriphenylcarbinol, and this method has been adopted in
the present work ; although in reality the carbinol bases have
little or nothing to do with the dyestuffs, so far as constitution is
concerned.

The simpler basic triphenylmethane dyestuffs are derivatives of

106 CHEMISTRY OF ORGANIC DYESTUFFS.

diamidotriphenylmetliane. This compound gives a violet dyestuff
on oxidation, which has not heen submitted to a close investiga-
tion [2] . It is probably a member of the class of compounds in
question, and has the constitution :

/C.H^NHs

The tetramethyl derivative of the above compound comes next
in the series, and is a well-characterized substance.

Tet7'amethyldiamidotriphenylcarhinol [3, 4, 5].

,CcH4N(CH3)o
C,H,N(CH3)2*

.CcH4N(CH3)

The base, separated from its salts by alkalies, forms a colourless
or slightly grey powder. It crystallises from ligroi'n in shining
colourless leaflets, or in round aggregates of crystals, M.P. 120°.
With acids the compound forms intensely green salts, water
being split oft*. As the amido-groups contain no replaceable
hydrogen, and as it is scarcely probable that the hydrogen neces-
sary for the formation of water is withdrawn from the methyl
group, it may be accepted that the hydrogen atom is displaced from
a molecule of the acid, and that the salt formed has a similar con-
stitution to the salts of quaternary ammonium bases. Accord-
ingly the hydrochloride has the constitutional formula [3] :

C jj _(./CgH4N(CH3)2

' ' f^CeH4N(CH3);

With a large excess of acid, the pale yellow diacid salt may be
obtained. The monoacid salts are characterized by the ease with
which they crystallise ; they are beautiful green dyestuffs of great
tinctorial power [5] .

TRIPHENYLMETHANE DYESTUFFS. 107

Hydrochloride, 0231124^2,1101, forms easily soluble green leaflets.

Sulphate, Co3Ho4N2,H2S04, crystallises with one molecule of
IL,0 in brilliant green needles, or anhydrous in thick green
prisms.

Zinc chloride double salt, (Co3Ho4N2,01)3 + 2ZnCl2 + 2H2O, forms
biilliant green needles or leaflets.

Oxalate, 2O23H24N2 + 3O2H3O4, large green prisms, easily soluble
in water.

Picrate sparingly soluble, crystallises in golden-yellow needles.

Ethyl ether,

OeH,C=rCoH,N(CH3)2]2,

I
OO2H5

is obtained by heating the base with alcohol to 110°; it is
colourless, and melts at 162°.
The methyl iodide [5J,

C23H25(OOH3)N2,20H3l + H2O,

is formed by heating the base with methyl iodide and methyl
alcohol. It forms colourless needles.

Tetramethyldiamidotriphenylcarbinol, or more correctly its
anhydride, is formed by oxidation of tetramethyldiaraidotriphenyl-
methane [3], and by condensation of two molecules dimethyl-
aniline with one molecule benzotrichloride in presence of zinc
chloride [4]. It may also be obtained from benzoyl chloride
and dimethylaniline [3] by action of the air.

The most recent method of preparation is by action of dimethyl-
aniline on the chloride obtained by treating dimethylamido-
benzophenone with phosphorus trichloride.

^^^ /CAN (0113)2

The salts of tetramethyldiamidotriphenylcarbinol come into
commerce under numerous names, of which Malachite Green and
Benzaldehyde Green are most usual. Malachite green has at-
tained considerable importance ; it has almost treble the tinctorial
power of the older methyl green, and possesses further the

108 CHEMISTRY OF ORGANIC DYESTUFFS.

advantages of dyeing wool easily and resisting the action of heat.
The oxalate and the zinc-chloride double salt are most frequently
met with.

Malachite green was first prepared by E. and O. Fischer [3]
by oxidation of tetramethyldiaraidotriphenylmethane. Shortly
afterwards Doebner obtained it by action of benzotrichloride on
dimethylaniline, a process which was patented [4, 6] and used
for the manufacture of the dyestuff. At that time Fischer's
method of preparation was not practicable, as the necessary benz-
aldehyde could not be obtained. However, the difficulties
encountered in the technical production of the latter were soon
overcome, and now the benzotrichloride process, which gives very
unsatisfactory results, has been entirely abandoned. At present
the manufacture of malachite green is carried out as folloAvs : —

The leuco-base is prepared by lieating one molecule of benzalde-
hyde with two molecules of dimethylaniline in presence of hydro-
chloric acid. (Zinc chloride was formerly used, but has been
found to be unnecessary.) The base is then dissolved in the
theoretical quantity of hydrochloric acid and the calculated
amount of finely suspended lead peroxide added to the solution,
which must be very dilute. The lead is removed as sulphate by
adding sodium sulphate, and the dyestuff precipitated by adding
zinc chloride and salt.

Nitro-derivatives of Tetramethyldiamidotriphenylcarhinol

[3, 8].

The paranitro-compound is obtained by oxidation of nitro-
tetramethyldiamidotriphenylmethane (from paranitrobenzalde-
hyde and dimethylaniline) and also by action of paranitro-
benzoyl-chloride and atmospheric oxygen on dimethylaniline [3] .

The base, C23H25N20(N02), crystallises in yellow prisms. The
salts are green, and are decomposed by water. On partial
reduction a violet dyestuff (probably tetramethylpararosaniline)
is formed; complete reduction yields tetramethylparaleucaniline.

The meta-compound [2, 8] is formed by oxidation of the nitro-
tetramethyldiamidotriphenyimethane obtained from metanitro-
benzaldehyde and dimethylaniline. It is similar to the former
compound, but does not yield a violet dyestuff on reduction.

TRIPIIENYLMETHANE DYESTUFFS. 109

Bichlortetramethyldiamidotriphenylcarhinol [11].

C23H24N2CI2O.

The salts of this compound come into commerce as Victoria
Green 3 B or New solid Green 3 B. It is prepared by condensa-
tion of dichlorbenzaldehyde with dimethylaniline and subsequent
oxidation of the leuco-base formed. Its shade is bluer than that
of malachite green.

Tetraethyldiamidotriphenylcarhinol [7] .
C27H32N2O.

The salts of this base come into commerce under the names
Brilliant Green^ New Victoria Green, Ethyl Green, and Solid
Green. The sulphate, C27H32N2,H2S04, is most commonly met
with. It forms brilliant, gold shimmering needles. The zinc-
chloride double salt forms brilliant green needles. In dyeing
brilliant green produces yellower shades than malachite green.

Sulphonic Acids [9, 10].

These bodies are in considerable demand, especially for wool-
dyeing, and numerous products are met with in commerce. They
are generally prepared by sulphonation of the leuco-bases, and
subsequent oxidation ; as the bases themselves do not give good
results on direct sulphonation. The sulpho-group enters especi-
ally easily into benzylatcd bases ; and probably enters the benzene
ring of the benzyl group.

Helvetia Green.

CasHasNsO^SNa.

This dyestuff, which is obtained by sulphonation of leuco-
malachite green, and subsequent oxidation, is the oldest of its
class ; but is not much used at present, as its acid properties are
only slightly developed.

110 CHEMISTRY OF ORGANIC DYESTUFFS.

Light Green S.

CsrHasN^OioSsNa.

This dyestuff is known also as Acid Green, Ligbt Green S F,
and Guinea-Green B, and is the most important of this class. The
leuco-base used for its production is diethyldibeuzyldiamido-
triphenylmethane, obtained by condensation of ethylbenzyl-
aniline and benzaldehyde. The resulting body is sulphonated
and oxidised. Light Green S F dyes wool and silk from an acid
bath (Friedlander, B.B. 1889, p. 588).

Certain blue dyestuft's which belong to this class have recently
been introduced into the market. They are prepared by conden-
sation of dimethylaniline, diethylaniline, and cthylbenzylaniline
with metaoxy- or mcta-amidobeuzaldehyde. The resulting leuco-
bases have the formulae : —

/C,H,OH(m) /CeH,OH(m)

HC, or HC^ r CH T

\\[CeH,N(CH3) J. \ [c^^ycuh^X

The commercial dyestuffs known as Patent Blue iVand Super-
fine are lime-salts of the sulphonic acids, obtained by sulphonation
and subsequent oxidation of the above leuco-bases. The shades
produced are similar to those of indigo extract, and have the
advantage of greater fastness and brilliancy (D. R. P. 46384,
48523; Chemikerz. 1889, p. 1702).

A further dyestuflP derivative of diamidotriphenylmethane is
Quinoline Green [1], obtained by action of tetramethyldiamido-
benzophenone, its chloride, or its hydrol on quinoline. In the last
case a leuco-compound is formed.

The dyestuff is probably constituted according to the
formula : —

C . CoH^N.

(CH3)2=NCeH,^

(CH3)2=NC6H/

II \

Acid Violet iVis a dyestuff of similar properties, and probably of
similar constitution to the above.

TRIPHENYLMETHANE DYESTUFFS. Ill

TriamidotrtphenTjlcarhinoU Pararosaniline.

/CcH^NHo
HaNCH^-C^

The anhydride occurs only in the coloured salts ; for example,
in the hydrochloride : —

HoN-Cell,— C:f 0 4 2

i^CH.NHHCl

The amido-groups of pararosaniline are in the para position to-
the methane- carbon atom. It is formed by heating two molecules
of aniline and one molecule of paratoluidine [11] with arsenic
acidj mercuric chloride, or other oxidizing agents ; by partial
reduction of trinitrotripheuylcarbinol with zinc powder and
acetic acid [12] ; by oxidation 'of triamidotriphenylmethane
(paraleucaniline) [12] ; by heating aurine with ammonia to 120°
[12] ; and by heating pure aniline with carbon tetrachloride,,
ethylene chloride, or iodoform. It may also be obtained by
action of paranitrobenzaldehyde [14], paranitrobenzyl- and benzoyl
chloride [15], or paranitrobenzyl-alcohol on aniline.

The base forms colourless leaflets sparingly soluble in cold, more
easily in hot water. It combines with one molecule of acid to-
form salts of an intense red colour. With an excess of acid,
yellow triacid salts are formed, which are decomposed by water.

On reduction, pararosaniline yields paraleucaniline (triamido-
triphenylmethane) .

By heating with hydriodie acid in a sealed tube it splits up
into aniline and paratoluidine. Pararosaniline was discovered by
Rosenstiehl [16], and its constitution determined by E. and O.
Fischer [12]. The above constitutional formula is deduced from
the following facts : —

On treating with nitrous acid, pararosaniline gives a hexazo-
com pound, in which all three nitrogen groups are present as diazo-
groups (probably carbinol compound). On boiling with alcohol
this diazo-compound yields triplienylmethane, CigHig.

112 CHEMISTRY OF ORGANIC DYESTUFFS.

On partial reduction trinitrotriphenylcarbinol yields pararos-
aniline [12] ; paraleucaniline being formed on further reduction.

By action of paranitrobenzaldehyde on aniline in presence of
zinc chloride, nitrodiamidodiphenylmethane is formed; yielding
paraleucaniline on reduction [12] .

Pararosaniline is present in most commercial rosanilines. Its
salts are similar to those of the latter, but are in general somewhat
more easily soluble in water.

The synthesis of pararosaniline (from paranitrobenzaldehyde,
&c.) [14, 15, 17, 18] has until now not been carried out on a
large scale, but it may be expected that in course of time the
technical difficulties which stand in the way of these processes
will be overcome. Recently pararosaniline has been manufactured
by a synthetic process leased on the following lines. Anhydroform-
aldehydeanilinc, obtained by action of formaldehyde on aniline,
is heated with aniline and aniline hydrochloride, whereby diamido-
diphenylmethane is formed. This latter compound, on heating
•with aniline, aniline hydrochloride, and an oxidising agent yields
pararosaniline.

Methyl Violet [19].

The commercial products known under this name are prepared
by oxidation of dimethylaniline sometimes containing monome-
thylaniline. The dimethylaniline is mixed with sulphate or chlo-
ride of copper, acetic acid, potassium chlorate, and a large quantity
of common salt. A more recent process consists in using phenol
in place of acetic acid — the chlorate being generally dispensed
with. During the actual process the cupric chloride becomes re-
duced to cuprous chloride, which oxidises again at the expense of
the chlorate or by the atmospheric oxygen, thus acting as oxygen-
carrier. Cuprous chloride is capable of forming an almost in-
soluble double chloride with methyl violet, this property being
absent in cupric chloride. Formerly the double compound was
decomposed by sulphuretted hydrogen, the soluble violet being
separated from copper sulphide by filtration. At present the
same end is attained by addition of ferric chloride, which oxidises
the cuprous salt to cupric chloride, which remains in the mother-
liquor after the violet has been salted out.

TRIPHE.VYLMETHANE DYESTUFFS. 113

The following will give an idea how the phenol process is carried
out on a large scale. The operation takes place in a drum, which
is jacketed, and connected with steam- and cold-water supplies.
Finely powdered salt and copper sulphate are stirred with phenol
and a little water to a homogeneous mixture. Dimethylaniline is
then added, and the whole heated to 55°^ with continual stirring,
care being taken that the temperature does not rise above 60°.
After a few hours the cover is removed, to allow the air to act,
the temperature being maintained at 55°. The process is ended
in about 8 hours, and the melt is cooled by passing cold water
into the casing of the drum. The melt is dissolved in water, and
the base of the dyestuft" precipitated, along with copper oxide, by
addition of milk of lime, and the precipitate washed to remove
soluble salts. It is then suspended in water, and treated with
sulphuretted hydrogen, whereby copper sulphide is formed, and
being insoluble in liydrochloric acid, the violet may be obtained in
solution by heating the precipitate with this acid. Finally, the
dyestuff is precipitated from the acid solution by salt, and purified
by repeated solution and reprecipitation by salt.

An older process, now abandoned, possesses interest from a
theoretical standpoint. In this case no chlorine compound was
used, the mixture consisting of dimethylaniline, copper sulphate,
acetic acid, and sand. The violet is precipitated from the solution
of the melt as sulphate by sodium sulphate. The absence of
chlorine prevents the formation of the insoluble double chloride,
and the reduced copper compound is got rid of as insoluble suboxide.

The rdle played by the phenol in the modern process of manu-
facture has not been explained, but it is certain that its presence
considerably increases the yield of the dyestuff.

Methyl violet is produced by action of other oxidising agents
on dimethylaniline, such as iodine and chloranil. According to
Brunner and Brandenburg bromine acts on dimethylaniline, form-
ing a brominated methyl violet [21]. On the other hand, the dye-
stuff is not produced by oxidation of dimethylaniline in acid solu-
tion, with lead peroxide, manganese dioxide, or chromic acid.

As yet, the chemistry of the methyl-violet process is little
understood. According to E. and O. Fischer [12], a methyl
group is partly oxidised, and the formic acid produced thereby
serves to link the benzene nuclei together, and to supply the
necessary methane-carbon atom. As, however, the formation of

114 CHEMISTRY OF ORGANIC DYESTUFFS.

violet is difficult to follow, it is not easy to give an explanation of
the reactions involved in its production.

In fact O. Fischer and Koerner have obtained hexamethylpara-
leucaniline quantitatively by action of the methyl ether of ortho-
formic acid on dimethylaniliiie [22] . The violet from dimethyl-
aniline and chloranil is apparently identical with the ordinary one
obtained by the copper process [23] .

Methyl violet forms amorphous masses with a green lustre. It
is easily soluble in Avater, and dyes wool and silk violet from
a neutral bath. On addition of a mineral acid^ the solution of the
violet becomes first blue, then green, and finally dirty yellow.

The commercial product is a mixture, consisting chiefly of
pentamcthyl- and tetramethyl-pararosaniline with some hexa-
methylpararosaniline.

If prepared from dimethylaniline containing monomethylaniline,
the violet also contains lower methylated rosanilines.

As the blue shade of the violet increases with the number of
methyl groups, the bluest brands are richest in hexamethyl com-
pounds. Blue shades of violet are also obtained by action -of
benzyl chloride on the violet-base. According to Fischer the
benzyl group does not attack hexamethylpararosaniline, only the
lower methylated products yielding benzylated violets [25] .

The dyestuffs known as acid-violets are mostly sulphonic acids
of benzylated methyl violets.

Methyl violet is difficult to convert into sulphonic acid by fuming
sulphuric acid ; a better result is obtained by sulphonation, and
subsequent oxidation of the leuco-base. Benzylated violets, how-
ever, are much easier to sulphonate, especially in form of their
leuco-bases, the sulpho-group probably entering the benzene
nucleus of the benzyl group. Other acid-violets are obtained by
methylation and benzylation of acid magenta.

Tetrametliylimrarosaniline [24] .

/C6H4N(CH3)2

This violet dyestuff was prepared by Fischer by oxidation of
tetramethyltriamidotriphenylmethane ; it is also obtained by
partial reduction of paranitro-malachite green.

TRIPHENYLMETHANE DYESTUFFS. 115

Acetyltetrametlrylpararosaniline [23],

/C6H4N(CH3)2
(CH3) 2N— C«H,— C\^ ^^^^ „ Q ,

is formed by oxidation of acetyltetramethylparaleucaniline. It is
a green dyestuft', and on treating with hydrochloric acid yields
tetramethylpararosaniliue.

Pentamethy JjiararosaniUn e [25].
(CHaj^N— CeH,-C<

^/CeH,N(CH3)2
'^C6H4NCH3

The pure base is obtained by saponification of its diacetyl deri-
vative Avitli hydrochloric acid. The hydrochloride is a constituent
of commercial methyl violet.

JJiacetylpentamethylpararosaniline [25].

[(CH3)2NCoHJ,=C— C^H^NCHs . C2H3O

I
OC2H3O

]May be obtained by treating the crude base of methyl violet with
acetic anhydride. It is a colourless base, and gives a green salt
Avith acetic acid. This fact is not easily understood unless under
the assumption that one acetyl group splits off, and the oxygen
atom of the carbinol group is eliminated.

Hexamethyljpararosaniline [23, 25, 26].

^Cl

[(CH3) 2NCeH,] 2 = C-CeH,N(CH3) ,
This dyestuff is known in commerce as Crystal Violet, and also
occurs in Methyl Violet. It is obtained by action of dimetliyl-
aniline on tetramethyldiamidobenzophenone :

(CH3)2NC6H,— CO-CeH,N(CH3)2

in presence of a dehydrating agent, according to the equation

Ci;H2oN20 + C8HuN,HCl = C25H30N3CI + 11,0.

This is effected on a large scale in one operation, phosgene
(COCI2) being allowed to act on dimethylaniline in presence of

116 CHEMISTRY OF ORGANIC DYESTUFFS.

zinc chloride, and further is formed by action of perchlormethyl-
formiate on dimethylaniline in presence of aluminium chloride or
zinc chloride. It is also produced by heating its methyl chloride
or methyl iodide compound (methyl green) to 110°-120°,

The hydrochloride and zinc double salt form lustrous green
crystals.

The hydriodide and picrate are sparingly soluble.

On reduction it yields hexamethylleucaniline, which forms
leaflets, M.P. 173°.

Hexaetliylpararosaniline.

-n/Cl

[(C<>H5)2-N-CeHj2-C-C,H,-N(C2H,

Tliis dyestuff comes into commerce as Ethyl Purple, and is pre-
pared by the action of phosgene on diethylaniline. It dyes bluer
shades than Crystal Violet.

Azo-Green.

OH
(CH3)2-N— CeH4-C/^«^4-"^=^— ^«^<C0
rCeH,-N(CH3)2

1 jL— ;-0

Although containing an azo-group, the tinctorial properties of
this clyestufF are due to its derivation from triphenyl-carbinol. It
is obtained by combining the diazo-compound from metamidotetra-
mcthyldiamido-tripheriylmethane with salicylic acid. It dyes
chromed wool a bright greenish-yellow shade. The corresponding
paramido-compound gives a blue dyestulF.

Methyl Green [19, 25].

,/CeH,N(CH3)2CH3Cl

(CH3)2N-C6H,-Cx^^jj^^,^^jj^^^

'>^1

(Clalormetliylate of Ilexametliylpararosaniline Chloride.)

This chloride or the corresponding iodide is formed by the action
of methyl chloride or iodide on commercial methyl violet. The
tetra- and penta-methylpararosanilines are converted into hexa-
methylrosaniline ; the latter adding on one molecule of methyl
chloride or iodide.

On a large scale methyl chloride is used. A slow stream of the

TRIPHENYLMETHANE DYESTUFFS. 117

gas is passed through an alcoholic solution of methyl violet heated
to 40°, and kept neutral by addition of soda. Autoclaves are un-
necessary, as methyl chloride is sutficiently soluble in alcohol and
no pressure is produced.

The alcohol is then distilled off, and the residue dissolved in
water, and unaltered violet precipitated by addition of soda or
chalk and common salt.

The pure zinc double salt of methyl green is then precipitated
by adding zinc chloride ; the precipitate being sometimes washed
with alcohol to remove any violet present. In commerce this zinc
double salt is generally met with in the form of brilliant green leaflets.

The iodide, C26H33N3I2, forms green needles easily soluble in
water [18].

The joecro^e,C2GH33N3[(CoH3)(N02)30H]2, is insoluble in water,
sparingly soluble in alcohol.

The base, C26H35N3O2, is obtained by treating the chlorine or
iodine compound with silver oxide. It is colourless^ and its
alcoholic solution remains colourless on acidifying, the formation of
a green salt only taking place on warnVing. The salts of methyl
green decompose at 110° to 120°, methyl chloride or iodide splitting
off, and leaving a violet residue of hexamethylrosaniline chloride.

An analogous green is the brom-ethylate obtained by the action
of ethyl bromide on methyl violet. The composition of the com-
mercial zinc double salt (ethyl green) is probably

C25H3,N3ClC2H5BrZnCl2.

An advantage of this ethyl green is that its shade is yellower than
that of methyl green. Methyl and ethyl greens dye silk directly,
and cotton prepared with tannic acid. Wool cannot be dyed
directly, and is either previously mordanted with sulphur by a bath
of thiosulphate of soda, or dyed in a bath of methyl green made
alkaline with ammonia. Fibres dyed with these greens become
violet on heating, and this reaction serves for their identification.
At present methyl and ethyl green are scarcely ever used, having
been replaced by the cheaper and stronger benzaldehyde greens.

The green colour of a compound appears to require the presence
of an ammonium group, and an amido-group not in combination
with an acid. Benzaldehyde green, for example, fulfils these con-
ditions. In methyl violet, an ammonium group and two methy-
lated amido-groups are present, and as long as the latter are not
in combination with an acid the compound is violet. When,

118 CHEMISTRY OF ORGANIC DYESTUFFS.

however, one of tliem is saturated by an acid, the colour changes
to green, but the green salts are unstable, and are decomposed by
water. Stable green dyestufFs are formed, if the acid is replaced
by methyl chloride, the same effect being produced by the intro-
duction of an ethyl group. It appears, therefore, that the neutral-
isation of the basic properties of the third nitrogenous group has
the same effect as its entire removal would have.

Triamidodiphenyltolylcarhinol [12, 28].
(RosANiLiNE, Magenta, Fuchsine.)
HgN^Q jj ^/CcH4NH2

Rosaniline, a homologue of pararosaniline, is formed by oxida-
tion of equal molecules of orthotoluidine, paratoluidine, and
aniline. As oxidising agents, stannic chloride, mercuric chloride
or. nitrate, arsenic acid, or nitrobenzene may be used. Mercuric
nitrate, arsenic acid, and nitrobenzene have been applied on a large
scale ; but at present the two latter are the only oxidants used
technically. The arsenic acid process is carried out in a boiler
fitted with a stirrer, and connected with a cooling- worm. Aniline
of approximately the above composition (aniline for red) and
syrupy arsenic acid (containing about 70 per cent, arsenic anhy-
dride) are introduced, and the mixture is heated to 170°-180°.
Part of the aniline oil used distils over during the operation,
which generally lasts 8 to 10 hours. As soon as the melt has
attained a certain condition, it is allowed to flow out, and after
cooling is broken up. It is then boiled with water in a closed
vessel under pressure, the arsenic and arsenious acids being at
the same time partly neutralised by addition of lime. After
filtering, the rosaniline hydrochloride is separated from the filtrate
by addition of salt. It is purified by recrystallisation. Magenta
prepared by this process generally contains arsenic. In the nitro-
benzene process, aniline for red is heated with hydrochloric acid,
nitrobenzene, and iron, the process being carried out in much the
same manner as above. The iron serves to start the process, by
forming ferrous chloride, which is oxidised to ferric chloride by
the nitrobenzene, which latter salt in turn effects the oxidation of
the aniline.

TRIPHENYLMETHAXE DYESTUFFS. 119

Nitrobenzene appears to take no part in the formation of ros-
aniline, and simply acts as oxidant, being converted to dyestufFs
of the induline class. AVhen nitrobenzene is replaced by chlor-
nitrobenzene, rosaniline is produced, and not, as might be expected,
a cldoro-dcrivative. Dyestuffs of the rosaniline series are formed
by oxidation of numerous bases in presence of aniline and parato-
luidine. Rosenstiehl and Gerber divide the homologues of aniline
into three classes, according to their behaviour on oxidation with
arsenic acid.

The first class includes bases which do not yield a magenta on
oxidation alone, but do if oxidised in presence of aniline. These
bodies are paratoluidine, asymmetric a-metaxylidine, cumidine,
and amidotetra- and amidopenta-methylbenzeue.

The second class comprises those bases which yield no magenta
on oxidation with arsenic acid, but do so if oxidised in presence of
a base of the first class. These bases are aniline, orthotoluidine,
and y-metaxylidine. The bases of the third class, metatoluidiue
and /3-metaxylidine, do not yield magenta under any conditions.

In the first class, one methyl group h in the para- position to the
amido-group, while in the second and third classes the para position
is free. In the second class the groiips are in the ortho position,
and in the third class in the meta position to the amido-group.
E. and O. Fischer^s experiments have proved that, in the simplest
rosaniline, the three amido-groups are in the para position to the
fundamental carbon atom. The complete analogy of the homo-
loguous rosaniliues with the first having been proved, it can be
readily understood why the members of the first group, when
oxidised by themselves or with each other, do not yield rosaniline,
but do so in presence of aniline.

In the bases of the second class, the para position is free, and
one or two ortho positions are occupied. It is clear that these
bases cannot yield rosaniliues unless they are oxidised with a base
of the first group. Neither can the bases of the first class pro-
duce magentas, but no reasons yet given can explain why they
should not be able to produce rosaniliues, when oxidised with other
members of the first class. The experiments of Monnet, lleverdin
and Noelting and O. Fisclier and Koch have, however, confirmed
this experiment. Noelting has recently extended our knowledge
of the behaviour of the homologues of aniline in this direction.
He examined bases in which both the meta and ortho positions are
occujjied, and found that such bases do not yield magenta under any

120 CHEMISTRY OF ORGANIC DYESTUPFS.

conditions, and therefore belong to the third class. Metamethy-
lated paratoluidines yield magenta on oxidation in presence of
aniline, whether the ortho position be occupied or not.

The investigations on this subject are best summarised as
follows : — All paramethylated anilines, paratoluidine, a-metaxy-
lidine, «-orthoxylidine, mesidine, pseudocumidine, isocumidine,
the cnmidine of Noelting and Forel, isoduridine, phrenidine, and
pentamethylamidobenzene yield magentas on oxidation with two
molecules of aniline, orthotoluidine, or v-metaxylidine, but do not
if oxidised with para free but methylated anilines as metatoluidine,
paraxylidine, v-orthoxylidine, s-metaxylidine, the cumidines of
Edler and Mayer, and crystallised duridine.

The commercial dyestuflF is the hydrochloride of rosaniline ; the
acetate, however, is also sometimes met with. The free base is
also prepared for the manufacture of aniline blue.

jRosaniUne-hase [28].
C20H21N3O.

Free rosaniline crystallises in colourless leaflets, which become
red on exposure to the air. It is sparingly soluble in cold water,
somewhat more easily in hot water, and still more easily in
alcohol. It is sparingly soluble in ether.

Rosaniline is capable of expelling ammonia from a boiling solu-
tion of ammonium chloride^ while in the cold rosaniline is preci-
pitated from a solution of its salts by ammonia.

The base is obtained technically by boiling the hydrochloride
(magenta) with the calculated amount of lime or caustic soda, and
a large quantity of water. The filtered solution deposits the base
on coolnig, in form of colourless leaflets which become brownish
on exposure to air.

By heating with water to 235°, rosaniline decomposes^ yielding
phenol, ammonia, a base C20H00N0O2, M.P. 176°, and an acid
C20H19NO3 [25]. At 270° ammonia, phenol, and dioxybenzo-
phenone HO— CeH^COCeH^— HO are formed [26] .

The salts [24] of rosaniline, like those of pararosaniline, are
formed with a simultaneous elimination of water. The monoacid
salts have an intense red colour ; the diacid salts are yellowish-
brown [24]. The salts are converted into a tertiary diazo-
compound by the action of nitrous acid [12] .

Hydrochloride^ C2oHi9N3,HCl + 4H20, occurs as large octohedra

TRIPHENYLMETHANE DYESTUFFS. 121

or rhombic tables^ wliicli have a green metallic reflex. It is with
dithculty soluble in cold water, easily iu hot water and alcohol.

Acid salt, C20HX9N3, (HC1)3, forms brownish-yellow needles,
easily soluble in water, and decomposed by an excess, or at lOC^.

Platinum salt, (C2oH2oN3Clo)(PtCl4)3.

Hi/ dro bromide, C2oHi9N3,HBr, is sparingly soluble.

Sulphate, (C2oHis)N3)2H2S04, forms brilliant green crystals,
sparingly soluble in water.

Acetate, C2oHi9N3,C2H402, forms large green crystals, easily
soluble in water.

Picrate, C2oHigN3,C6H2(K02)30H, forms needles, sparingly
soluble in water.

The tannate forms a red precipitate insoluble in water.

Rosaniline and pararosaniline form colourless unstable com-
pounds with sulphurous acid and bisulphites. These compounds
react with aldehydes, forming peculiar dyestufFs (Detection of
Aldehydes [29]).

Bosanilinestdplionic Acid [30].
(Magenta S, Acid Magenta.)

By the action of strong fuming sulphuric acid on magenta at
120°, a sulphonic acid, probably the disulphonic acid, is formed.
This acid has an intense red colour, and the solutions of its salts
are not turned yellow by acids like those of magenta. The neutral
salts, with the alkalies and metallic oxides, are colourless, the acid
salts being red. Both are easily soluble in water, and difficult to
crystallise. From the colour of the acid it is probable that the
sulplio- and amido-groups are combined to form a salt, while the
colourless salts contain the carbinol group.

Rosanilinesulphonic acid dyes wool and silk from an acid bath,
and finds extensive application in dyeing.

Tetrahromrosaniline [31]

is formed by the action of bromine on rosaniline. It is a colour-
less base, forming violet salts.

At present the researches of E. and O. Fischer and others have
led to some confusion as to the exact composition of the metliyl-
rosanilines examined by Hofmann. If methyl green is hepta-

122 CHEMISTRY OF ORGANIC DYESTUFFS.

methyl pararosaniline, iodine green is not penta- but heptamethyl-
rosaniline, and the violet formed on heating is hexamethylrosa-
niline. The analytical results obtained by Ilofmann scarcely
admit of this interpretation. In the present work these bodies
are described under the older formulae, with the hope that further
researches may elucidate the matter.

Trhnethylrosaniline [28],
C2oH,s(CH3)3N30.

Thehydriodide^ CosHngNgljis formed by heating rosaniline with
methyl iodide and methyl alcohol. It is a violet dyestuff sparingly
soluble in water.

Tetramethylrosanilwe [28],

C2oHi;(CH3),N30,

is obtained by heating iodine green to 120°. The iodide,
C24H2SN3I, forms long bluish-violet needles.

Pentamethylrosaniline [32]. (Iodine Greex.)

1\ie. iodide, C2oHi7(CH3)4N3l,CH3l + H20, is prepared by heat-
ing rosaniline Avith methyl iodide and methyl alcohol to 100°. It
is freed from any violet dyestuff present in the same manner as
methyl green.

The iodide forms metallic i)risms easily soluble in water. When
heated to 100°-120° methyl iodide splits off, leaving tetramethyl-
pararosaniline.

The zinc double salt, C2.5HsiN3Clo,ZnCl2, forms large green
crystals. Its solutions are turned yellowish-green by acids.

The joicra/e, C25H29N3C6H3(N03)30, forms prisms with a coppery
reflex, which are insoluble in water and sparingly soluble in alcohol.

Before the introduction of methyl green, iodine green was ex-
tensively used in dyeing.

Ilexamethylromniline [32].

The iodide, C2oHi4(Cri3)gN3l, is formed along with octomethyl-
leucaniline by heating iodine green with methyl alcohol in a sealed
tube to 100°. It forms brownish-green needles, insoluble in water
and sparingly soluble in alcohol. It is a violet dyestuff.

TRIPHENYLMETHANE DYESTUFFS. 123

Triethylrosaniline [28]. (Hofman.n's Violet.)

C20Hi8(CoH,)3N3O.

The iodide^ C26H3.5N3I2, is obtained by heating rosaniline with
etliyl iodide and alcohol. It forms brilliant green needles, soluble
in alcohol and sparingly so in water. It was formerly manufac-
tured on a large scale.

Tetraethylrosaniline [28].
The iodide has the formula CooHi(;(C2H5)4N3l.

Trihenzylrosaniline-metliyliodide,
CsoHietCrHr) 3N3CH3I,

is prepared by treating rosaniline with benzyl chloride, methyl
iodide, and methyl alcohol. It forms green needles insoluble in
water [33].

Acetylrosaniline [34],

C20Hi8(C2H3O)N3,

is formed when rosaniline hydrochloride is heated Avith acetamide.
It dissolves in alcohol with a red colour, and forms violet salts.

TriacetylrosaniUne [35],

C2oHi6N3(C2H30)3,

and Trihenzoylrosanili7ie [35],

C2oHicN3(C7H,0)3,

are obtained by the action of acetyl chloride and benzoyl chloride
respectively on rosaniline. They are colourless bases forming
orange salts.

Compounds of rosaniline v/ith aldehydes have been described by
H. Schiff (Ann. cxl. p. 101).

The yield of magenta obtained on a large scale by either of the
processes already described is very poor, and seldom exceeds 33
per cent, of the weight of the bases employed. A large quantity
of bye-products is formed, and little is known as to their nature.
A constant product of the arsenic acid process is a small quantity

124 CHEMISTRY OF ORGANIC DYESTUFFS.

of chrysaniline. Besides this, various violet and bluisli-black pro-
ducts are formed, some of which are soluble in water, some in
alcohol, and others are totally insoluble. Some o£ these dyestuffs
dissolve and remain in the mother-liquor of the magenta, but by
far the greater part occur in the insoluble residue. From the latter
Girard, Delaire, and Chappotot [36] have isolated three bases, viz. : —
mauvaniline, C19H17N3, violaniline, CigHigNg, and chrysotoluidine,
C21H21N3. However, sufficient analytical data are not forthcoming
to support these formulae, and it is doubtful whether the products
examined were really chemical individuals. Possibly violaniline is
identical with the simplest induline, and chrysotoluidine with
chrysaniline, especially as dyes of the induline series occur in the
the magenta-residues (see Indulines).

Aniline Blue [37].

Aniline reacts with rosaniline at 180° in presence of certain
organic acids, ammonia being evolved, and phenyl-groups entering
into the rosaniline molecule. According to tjjc number of phenyl-
groups introduced, the shade of the compound produced varies
from violet to pure blue. It is not possible to introduce more than
three phenyl-groups into the rosaniline molecule. Acetic acid,
benzoic acid, and stearic acid have been used technically^ but at
present benzoic acid alone is used, as by its aid the best results are
obtained both as regards yield and shade of blue (greenish). The
action of organic acids in the blue process has not yet been ex-
j)lained. Rosaniline heated with aniline without an organic acid
does not yield a blue ; a blue is, however, formed from rosaniline
and paratoluidine. Only a minute quantity of benzoic acid is
required to effect the formation of blue, but in presence of a
larger quantity the results are better, and the process is more
rapid. At the end of the reaction, benzoic acid remains in the
melt unaltered, and may be almost entirely recovered by extrac-
tion with alkali.

The amount of aniline used in the manufacture of blue is of
great importance. In presence of a large excess of aniline the
phenylation is more complete and rapid than when a small quan-
tity is used. For production of pure triphenylrosaniline (green
shade of blue) a large excess of aniline is used (ten times the
theoretical amount) along with a correspondingly large amount of

TRIPHEXYLMETIIAXE DYESTUFFS. 125

benzoic acid. The higher homologues of aniline, especially ortho-
toluidine, give redder shades of blue, and it is therefore necessary
to use an aniline as pure as possible. It is required that commer-
cial '^ aniline for blue " should distil within one degree, and is thus
almost chemically pure aniline. For the manufacture of a reddish
shade of blue, smaller quantities of benzoic acid and aniline are
used, and a less pure aniline-oil is applicable. On a large scale
aniline blue is prepared approximately as follows : —

The mixture of the requisite quantities of rosaniline base, ben-
zoic acid, and aniline is brought into a vessel fitted with stirrer
and distilling arrangement, and heated to the boiling-point of the
aniline. As the blue is contained in the melt in form of the
colourless base the progress of the reaction cannot be ascertained
by simple inspection. For this purpose portions are removed from
time to time, and dissolved in alcohol and acetic acid, the operation
being interrupted as soon as the test shows that the desired shade
has been reached. According to the shade of blue required, the
process may last two to four hours, but if the heating is protracted,
some of the blue is liable to be destroyed.

On partly saturating the melt with concentrated hydrochloric
acid, the hydrochloride of triphenylrosaniline separates out almost
in a state of chemical purity, while impurities remain dissolved
in the concentrated solution of aniline in aniline hydrochloride.
This latter is separated and saturated with dilute acid, and the
precipitate is worked up for inferior blue. This method of purifi-
cation has completely replaced the older process with alcohol.

The salts of the lower phenylated rosanilines dissolve easily in
alcohol, while those of triphenylrosaniline are very sparingly
soluble. A very large number of marks of blue come into com-
merce, the shades being influenced firstly by the degree of phenyla-
tion, and secondly by the number of sulpho-groups introduced for
the production of soluble blue. Other brands, again, are obtained
from the lower quality of blue already mentioned.

i. Monoiihenylrosaniline.

C2oH2oN3(CeH5)0.

The hydrochloride forms brilliant bronzy crystals, soluble in
alcohol with a reddish- violet colour [39].

126 CHEMISTRY OF ORGAXIC DYESTUFFS.

ii. Diphenylrosaniline.

C2oHi9N3(CeH,)30.

This base forms bluish-violet salts [28, 38] .

iii. Triphenylrosaniline. (Aniline Blue.)
CsoHigNg (CgHg) 3O.

The free base is colourless and easily soluble in alcohol [28,
37,38].

The hydrochloride, C2oHi7N3(C6H,5)3HCl, is the technical product
obtained first in the fractional precipitation of the blue melt with
hydrocliloric acid. In this state it forms brilliant green crystals,
insoluble in water and sparingly soluble in hot alcohol. Aniline
dissolves it somewhat more easily. The alcoholic solution has a pure
blue colour. Some of this product is used as " spirit-blue/' but
by far the greater quantity is used for the manufacture of soluble
blues. Triphenylrosaniline salts dissolve in sulphuric acid with a
brown colour.

The sulphate (CjoHigNs (06115)3112804) is almost insoluble in
alcohol.

iv. Sulphonic Acids of Tnphenylrosa7iiline.

The difficulties encountered in the sulphonation of rosaniline
are altogether absent in that of the phenylated rosanilines. A
monosulphonic acid is formed by the action of concentrated sul-
phuric acid at a comparatively low temperature, while by a more
energetic sulphonation two, three, and even four sulpho-groups
may be introduced into the molecule.

From the foregoing it appears probable that the sulpho-groujis
enter the phenyl groups aiid not the rosaniline nucleus.

The sulphonic acids are all amorphous, and possess a blue colour.
The salts of the acids are, on the contrary, colourless and probably
carbinol derivatives.

Monosulphonic Acid.
C38H30N3SO3H.

This is the first product of the action of sulphuric acid on
aniline blue. The free acid is obtained as a blue amorphous

TRIPHEXYLMETHAXE DYESTUFFS. 127

precipitate, "which is iusohible in water. Tlie salts are colourless or
nearly so, are easily soluble in water, and cannot be crystallised.
The sodium salt forms the " alkali blue " of commerce.

This salt, unlike those of other sulphonic acids, may be fixed
on wool and silk from a slightly alkaline bath. It is probable that
the basic groups of rosaniline effect this fixation. The shade ob-
tained is not strong, but on development with dilute acid, whereby
the free sulphonic acid is liberated, a good blue shade is obtained.
Alkali blue finds its principal application in wool-dyeing.

Bisulplionic Acid,

C38H,,N3(S03H)2,

is a product of the further action of sulphuric acid on the above
acid. It is soluble in pure water, but insoluble in dilute sulphuric
acid, and may therefore be precipitated from the sulphuric-acid
solution by water.

It forms two series of salts with bases — acid salts, which have a
coppery reflex, and neutral salts, whibh are colourless. The acid
sodium salt is a commercial product, and is known as " water blue
for silk.''

Tri- and Tetra-sulphonic Acids.

These bodies result by continued action of sulphuric acid at a
higher temperature.

They are not precipitated from an acid solution by water, and
thus differ from the disulphonic acid. In order to isolate them,
the sulphuric-acid solution is neutralised with chalk, and the pre-
cipitated calcium sulphate filtered oif. The solution of lime-salt
is then converted into sodium-salt.

The dyestuff known as " soluble blue for cotton " is probably a
mixture of both acids, or rather of their acid sodium-salts.

All the " soluble blues " are dyed on wool and silk from a
bath containing sulphuric acid. Cotton is previously mordanted
with alum and soap, or with tannin and tartar emetic.

Another blue is obtained by the action of aniline and benzoic acid
on pararosaniline. This product is valued for the pure greenish
shade which it produces, and it has recently found extensive appli-
cation, and appears to have almost displaced diphenylamine blue.

128 CHEMISTRY OF ORGANIC DYESTUFFS,

Homologues of aniline blue have been prepared by the action
of toluidines on rosaniline. They possess a dull reddish shade.

Naplithylrosanilines are formed by action of the naphthylaraines
on rosaniline^ but^ like the above, possess no technical interest.

DipJienylamine Blue.
Girard and Delaire (Jahresber. 1867, p. 695).

Dyestuffs of a very pure blue shade are formed by the action of
oxalic acid or of hexachloride of carbon (CgClg) on diphenylamine.
On a large scale diphenylamine blue is prepared by heating
diphenylamine with oxalic acid to 110°-120°. The dyestuff
formed, which amounts to only 10 per cent, of the diphenylamine
employed, is purified by repeated treatment with alcohol. It comes
into commerce in the form of its higher sulphonic acids (soluble
blue), and finds its principal application in silk- and cotton-dyeing.

Similar dyestuffs, probably identical with diphenylamine blue,
are formed by treating methyldiphenylamine with oxidising agents,
as, for example, with chloranil [15] .

A dyestuff named Bleu de Mulhouse was prepared by Gros-
Renaud and Schaeffer by the action of alkaline shellac solution on
rosaniline.

Persoz, Deluyne, and Calvetet obtained (1861) a soluble blue dye-
stuff by the action of anhydrous stannic chloride on aniline (pure ?) .
The composition of this compound is not known, neither has it
been applied in practice [41] .

Aldehyde Green [43, 70, 71].

On treating rosaniline with aldehyde and sulphuric acid, a blue
dyestuff is formed, which, on treatment with sodium thiosulphate
in acid solution, yields aldehyde green. For its preparation, a
mixture of rosaniline, aldehyde, and sulphuric acid is heated, till
the product produces a blue- violet solution with water. It is then
poured into a very dilute sohition of sodium thiosulphate. Sulphur
and a grey compound separate, while the green remains dissolved.
It may be precipitated by addition of zinc chloride or acetate of
soda ; in one case a zinc double salt, and in the other a free base,
is obtained.

The chemistry of the reactions taking place in the preparation
of aldehyde green has been studied in detail with pararosaniline.

TRIPHENYLMETHANE DYESTUFFS. 129

In the first stages of the reaction a blue dyestuff, the so-called
aldehyde blue, is formed, along with a green dyestufF.

This blue has the composition of an anhydro-aldol-pararosani-
line,

/C6Hi-N=CH-CH.-CHOH-CH3

OH— C-C6H4-N=CH-CHo-CHOH-CH3

^C6H4-N=CH-CH2-CHOH-CH3,

and is incapable of yielding the green on treatment with a thio-
sulphate. The green dyestuff formed at the same time is a quin-
aldiiie derivative of the above dyestuff, and has the constitution

/CH=CH

/C^H,- N=C-CH3
OH-C-CgH^- N=CH-CH2-CHOH-CH3
CgH^- N=CH-CH2-CHOH-CH3.

The thiosulphate employed in the reaction enacts two functions.
It separates the above blue dyestuff, and at the same time converts
the green dyestuff into a new compounrl_, containing sulphur, which
is faster to light and dyes a better shade than the original green.
Two processes were originally in vogue for the production of alde-
hyde green. The process of Lucius consists in treating the mix-
ture obtained by the action of aldehyde and sulphuric acid on rosa-
niline with sulphuretted hydrogen and then with sulphurous acid,
while in that of Usebe the agent employed is a thiosulphate. The
green dyestuffs obtained in these processes are both derived from
the above green, but differ in composition. The green obtained in
Lucius's process contains two atoms of sulphur, while that of
Usebe only contains one. Their constitutions are expressed by the
following formulae : —

CH = CH

/ I

/C6H,-N=CH-CH3

C-OH
\
XH4-NH-CH-CH2-CHOH-CH3

S
I

'CeH4-NH-CH-CH,-CHOH-CH3
Lucius' s Green.

130 CHEMISTRY OF ORGANIC DYESTUFFS.

CH = CH
/ I

/C6H4-N=C-CH3

C-OH

XH4-N-CH-CH0-CHOH-CH3

CgH^-N-CH-CHo-CHOH-CHs
Usebe's Green.

Of course, the products obtained from rosaniline contain one
methyl-group more than is expressed in the above formulae : its
position can only be a matter of speculation.

Aldehyde green is a basic dyestuff, and was largely used before
the introduction of iodine green. The zinc double salt came into
commerce as a paste, or the green was prepared by the consumers.
The tannate, obtained by precipitating the solution with tannic
acid, was used in printing, being used with acetic acid and fixed
by steaming.

Diphenylnaphthylmethane Lyestuffs [1].

Certain derivatives of diphenylnaphthylmethane similar to the
diphenylmethane derivatives already described are in use as dye-
stuffs.

Compounds of this class are obtained by the action of substi-
tuted naphthylamines on tetramethyldiamidobenzophenone in pre-
sence of dehydrating agents. In place of the latter compound its
chloride or the corresponding benzhydrol may be used.

Victoria Blue B is the product of the action of phenyl- a-naph-
thylamine on tetramethyldiamidobenzophenone in presence of
phosphorus oxychloride. The reaction is expressed by the follow-
ing equation : —

(CH3)2NCeH,COC6H,N(CH3)3 + CioH7NC6H5=C33H32N3 + H20.

The constitution of the dyestuff is represented by the formula

(CH3)3-N-CeH,s^^ CioHe-NHCeH,

(CH3) 2-N-CeH/ ^ < ^\C1 •

Victoria Blue 4 R. — This dyestuff is obtained by a similar
process with methylphenyl-a-naphthylamine. Its constitution is

TRIPHENYLMETHANE DYESTUFFS. 131

expressed by one of the following formuhe, the second being the
more probable, as it differs greatly in shade from Victoria Blue B.

I. /C-CioHsN^CHs

(CH3)o-N-CeH/ I 1 \C1

Night Blue is obtained from paratolyl-a-naphthylamine
( p-CyllyNHCioHy) and tetraraethyldiamidobenzophenone. These
dyestuffs come into commerce as hydrochlorides. They are
beautiful blue dyestuffs, easily soluble, and dye cotton prepared
with tannic acid similarly to methylene blue, but unfortunately
the shades produced are not very fast to light. In general their
reactions resemble those of the rosaniline dyestuffs. Alkalies
precipitate a reddish-brown base, and acids turn the blue colour
to yellow.

Victoria blue B base cannot be crystallised. In a pure state it
forms a brick-red powder; M.P. 95°.

Victoria blue 4 B. base has also not been obtained in a crystal-
lised state. It resembles the above in appearance, and melts at 77^^
[72].

B. ROSOLIC ACID DYESTUFFS.

These dyestuffs are closely related to those obtained from ros-
aniline, and may be regarded as rosanilines in which the nitrogen
is replaced by a group containing oxygen.

The actual dyestuffs, like rosaniline salts, are anhydrides of a
carbinol. For example, aurin, C19H14O3, is the anhydride of an
unknown carbinol, trioxytriphenylcarbinol : —

HOC,H,-C<CeH.HO ^i2j

The compounds of these series have an acid character, and in
the free state are yellow, while the salts dissolve in water with a
red colour. They cannot be fixed on textile fibres, and are con-
sequently almost useless in dyeing. Some of the colour-lake*
are used in paper manufacture and for colouring tapestry.

K 'Z

132 CHEMISTRY OF ORGANIC DYESTUFFS.

Aurin, Pararosolic Acid [12].

(HO-C,H4)o=C-C6HA

I I

Aurin is prepared by heating phenol with oxalic acid and
sulphuric acid : 6 parts of phenol, 8 parts sulphuric acid, and
4 parts of dried oxalic acid are heated for about twenty-four hours
to 120°-130°.

The melt is extracted with water, and the residue dissolved in
hot alcohol, and ammonia gas passed into the solution. The
precipitate which forms is boiled with acetic acid or hydrochloric
acid [44, 48, 49], Aurin is also formed by condensation of
phenol with formic acid and zinc chloride [45], by boiling the
diazo-compound from pararosaniline with water [12], by heating
dioxybenzophcnone chloride with phenol [46], and by action of
salicylic aldehyde on phenol in presence of concentrated sulphuric
acid [47].

Aurin forms dark red rhombic crystals or red needles with
a green metallic reflex. It decomposes without melting. It
dissolves in alcohol and glacial acetic acid with a yellowish-red
colour, and in alkalies with a magenta-red colour. It forms
soluble double compounds with bisulphites of the alkalies.

KHS03,Ci9Hi403 forms colourless leaflets, immediately decom-
posed by acids. Aurin further forms a very unstable compound
with hydrochloric acid. Reducing agents convert aurin to
leucaurin (CigHigOa) (trioxytriphenylmethane) . On heating with
aqueous ammonia to 120° it yields pararosaniline [13] .

It is decomposed by heating Avith water, phenol and dioxy-
benzophcnone being produced.

For bye-products of aurin manufacture see the original
article [49].

BosoUg Acid.

OHC«H, \^
C20H1GO3 = OH \p TT /C — CgH^.

"^ o

This body is formed on boiling the hexazo-compound of rosa-
niline (C30H19N3) with water [50], and may be obtained by

TRIPHENYLMETHANE DYESTUPFS. 133

heating a mixture of phenol and crcsol with arsenic acid and
sulphuric acid [49] .

The rosolic acid described by Runge (1834) as obtained from
the residue of crude phenol distillation is probably identical with
the body at present under consideration,

Rosolic acid forms infusible lustrous green crystals. It is
almost insoluble in water, but dissolves easily in alcohol and
acetic acid with an orange-red colour. Its alkaline solutions are
red. It gives colourless double compounds with bisulphites, and
in its general behaviour closely resembles aurin. On reduc-
tion, leucorosolic acid (trioxydiphenyltolylmethane), CaoHigOs, is
formed. Dioxyphenyltolylketon and phenol are products of its
decomposition with water [31].

Two other products obtained from aurin have also been used
to some extent in practice.

Red coralline [52] or Peonine is obtained by heating crude
aurin with ammonia under pressure, and' is probably intermediate
in composition between aurin and pararosaniline. Azulin is
obtained by action of aniline on auVin, and is probably an aurin
containing aniline groups [53] . This blue dyestuff was largely
used before the introduction of aniline blue.

Pittacal (Eupittonic Acid).

The formation of this dyestuff was first observed by Reichen-
hach in 1835. He obtained it by treating certain fractions of
beech-tar creosote with baryta- water in presence of air [54] .

The formation of similar blue products has also been noticed by
Graetzel, and the subject has been investigated by Liebermann and
by A. W. Hofmann.

Liebermann gave to his product the name Eupitton or Eupittonic
acid, but it is not certain that this body is identical with Reichen-
bach's Pittacal [55] . The constitution and method of formation,
of this body were determined by Hofmann [56] .

Eupittonic Acid, Hexamethoxylaurin [55].

C,9H8(OCH3)603.

This compound is obtained by action of carbon hexachloride on
an alkaline solution of two molecules of pyrogalloldimethyl ether

134 CHEMISTRY OF ORGANIC DYESTUFFS.

and one molecule of methylpyrogalloldimettiyl ether at 160°-170°.
It is also formed by action of air on an alkaline solution of both
ethers [56].

Eupittonic acid forms orange-yellow needles, insoluble in water
and soluble in alcohol and ether. It is a dibasic acid and
forms salts which have a blue colour in solution. They may be
precipitated by an excess of alkali. The salts of the heavy metals
are sparingly soluble blue lakes. Like aurin, eupittonic acid
gives unstable compounds with acids.

Dimethyl ether [56], C25H240<)(CH3)2, is formed by action o£
methyl iodide on the sodium salt. It forms golden-yellow needles.
M.P. 242°.

Diethyl ether [56], C25H240<,(C2Hg)2. M.P. 202°.

Diacctate [56], C2r,H2409(C2H30)2, yellow needles. M.P. 265°.

An analogous compound to eupittonic acid is obtained by oxi-
dation of pyrogalloldiraethyl ether with methylpyrogalloldimethyl
ether — Tetraoxyethyldioxymethylaurin [56] ,

Ci9Hs(OCH3)2(OC2H5),03.
This compound forms brick-red needles, soluble in ether,

Heocamethoxylpararosaniline [25],

C05H31N3O7 = Ci,Hi3 (OCH3) 6N3O,

is obtained by heating eupittonic acid with aqueous ammonia
under pressure to 160°-170°. The formation of this body is
analogous to that of par aros aniline from aurin. The base forms
hair-like colourless needles, which rapidly become blue on
exposure to the air. It is decomposed on heating with water,
eupittonic acid being regenerated, while ammonia splits off.

The monoacid salts of this base are blue and the triacid yellow.
The dyestuffs of this class are not of any technical value.

Aurintricarhonic Acid (Cheome-Violet) [73].

/CcH3(0H)C00H

OH— C-CeHaiOHjCOOH

'^C6H3(OH)COOH

This compound is obtained by oxidation of salicylic acid and
methyl alcohol in concentrated sulphuric acid solution with sodium
nitrite. It forms a red powder with greenish reflex, and produces

TRIPHENYLMETHANE DYESTUFFS. 135

briglit shades on metallic mordants. The chromium lake is fast
to soap. For the methyl alcohol may be substituted formaldehyde
or methylal, and homologous derivatives may be obtained by
replacing the whole or molecular portions of the salicylic acid by
^-cresotic acid.

Dyestuffs feom Benzoteichloride and Phenols.

Benzotrichloride^ according to Doebner [57], acts on phenols
in a similar manner to dimethylaniline. The dyestuffs formed
are related to rosolic acid in their constitution ; they are deriva-
tives of triphenylmethane and contain an oxygen atom linked to
the methane-carbon atom and one benzene ring. Throughout,
however, they contain one intact phenyl ring, the other two
containing oxygen. The simplest member of the class is formed by
interaction of two molecules of phenol and one molecule of benzo-
trichloride, and is called Benzaurin. Benzaurin stands in the
same relation to dioxytriphenylmethane as aurin does to trioxytri-
phenylmethane. Its constitution is accordingly the following : —

aH.HO.

I I

Benzaurin forms hard lustrous crusts. It is insoluble in water,
soluble in alcohol, ether, and glacial acetic acid, with a yellow
colour. It dissolves in alkalies with a violet colour, and is pre-
cipitated from its alkaline solution by acids. It forms soluble
double compounds with bisulphites,

Benzaurin dyes wool and silk yellow from an acid bath. It
yields dioxytriphenylmethane on reduction. This compound
crystallises from alcohol in yellowish needles.

Besorcinbenzein, C19H14O4, is an analogous body obtained by
action of benzotrichloride on resorcin. With bromine it gives a
tetrabrom-compound, which dyes silk a shade similar to that
produced by eosine.

Basic derivatives of the above bodies have been recently de-
scribed by Heumann and Rey [74].

These bodies, called Rosamines, are obtained by action of benzo-
trichloride on mono- or dialkyl derivatives of metamidophenol.
The new bodies are beautiful red to violet dyestuffs.

One of the simplest members of the series — tetramethylrosa-

136 CHEMISTRY OF ORGANIC DYESTUFFS.

mine — is prepared by heating one molecule benzotrichloride with
two molecules dimethylmetamidophenol in benzene solution^ or
mixed with sand, to about 60°,

The hydrochloride forms needles with a steely-blue reflex, and
dissolves easily in water with a beautiful bluish-red colour ; the
solution exhibits a bright yellowish-red fluorescence. Its consti-
tution is expressed by the formula —

CeH3N(CH3)2
>0

C6H3(CH3)2C1

Tetramethylrosamine dyes wool and silk in an acid bath, pro-
ducing shades from pink to dark bluish red.

The oxalate forms dark green needles and the nitrate steel-blue
needles.

By heating oxalic acid with resorcin and sulphuric acid, Baeyer
obtained a yellow dyestuff*, which is probably Euxanthone [58] .
According to Claus and Andreaj [59] it possesses the formula
Ci3Hf404, while Gukassianz obtained two bodies in the same
reaction, to both of which he ascribes the formula C14H8O5 [60] .
Rosicki [61] obtained a dyestufi" by heating resorcin with
isosuccinic acid and sulphuric acid. This body, Resorcin-isosuc-
cine'in, has the same composition as Brasilein, CkjHi^O^, and is
similar in its properties.

C. PHTHALEINS [62].

The phthaleins are derivatives of triphenylmethane, and form a
group of dyestuffs which are sharply defined from the rosaniline
and rosolic acid derivatives already described. In the latter the
chromophorous groups are in para positions, while in the former
two adjacent positions are taken up.

The chromophor of the phthaleins is the lacton ring : —

— C.
— CO^

TRIPHENYLMETHANE DYESTUPPS. 137

which occupies two adjacent positions in one benzene ring, one
carbon atom being linked to another benzene ring.

With respect to the colour-giving group, there is a certain
analogy between these dyestuffs and those of the Indigo series,
these latter being characterised by the lactam or lactim ring : —

C— CO C— COH

/ or .^

-NH -N

The phthaleins are all derivatives of phthalophenone, the inner
anhydride of tripheuylcarbinolcarbonic acid :

C6H5\p/OH CgHsxp //0\.ppw

Triphenylcarbinolcarbonic acid. Phthalophenone.

This acid is not capable of existing in a free state, but may be
obtained in form of its salts. The itelationship between phthalo-
phenone and triphenylmethane is easily determined. By treatment
with alkalies it yields triphenylcarbinolcarbonic acid, and this may
be converted to triphenylmethanecarbonic acid by reduction with
zinc powder. On heating this latter compound, carbon dioxide
splits off, forming triphenylmethane.

Phthalophenone is not a dyestuff, the tinctorial character only
becoming apparent on introduction of hydroxyl groups into both
phenyl groups.

The phthaleins (hydroxy lated phthalophenones) are almost ex-
clusively obtained by action of phenols on phthalic anhydride.

The position of the hydroxyl groups with reference to the
methane carbon atom has considerable influence on the character
of the dyestuff produced. With simple phenols, as, for example,
in the formation of phenolphthalein, the hydroxyl group is iu the
para position to the carbon atom.

Compounds of this class are mostly of little character as dye-
stuffs. They are colourless and only form coloured salts. Real
dyestuffs are only obtained from phenols which contain two
hydroxyl groups in the meta position, such as rcsorcin and pyro-
gallol. Probably here also the condensation takes place in a
para position to one hydroxyl group, and is therefore ortho to the

138 CHEMISTRY OF ORGANIC DYESTUFFS.

other. The condensation is generally attended by the formation
of an anhydride between two hydroxyl groups.

The phthaleins, with exception of rhodamine, are acid dye-
stuffs.

The chromophor of the phthaleins is of a strong acid character,
and thus intensifies the acidity of the hydroxyl groups, and this
eflFect may be considerably increased by introduction of halogens
or nitro-groups into the benzene rings. The halogens exert con-
siderable influence on the shade of the dyestuffs.

The coloured phthaleins are converted into colourless phthalins
on reduction, these latter bodies being the corresponding deri-
vatives of triphenylmethanecarbonic acid.

On treating with energetic dehydrating agents, most phthaleins
are converted into anthraquinone derivatives, one molecule of
phenol being split off during the reaction [62] .

The phthaleins are very numerous, and only those of value
from a technical or theoretical point of view are considered
here.

Phenolphthale'in [62]. Dwxyphtlialo]phenonet

(OHC6H4)2=C— 0\

I CO.

This body is obtained by action of phenol on phthalic anhy-
dride in presence of strong sulphuric acid. The free phthalci'n
forms colourless crystals, melting at about 250°; it dissolves in
alkalies with a red colour, and is precipitated by acids as a white
precipitate. The alkaline solution is decolorised by excess of alkali.
On melting with caustic potash, it yields benzoic acid and dioxy-
benzophenone. On account of the change in colour occasioned by
free alkalies (not carbonate or ammonia), phenolphthalein is useiul
as an indicator in titration.

TRIPHENYLMETHANE DYESTUJFS. 139

Fluorescein [62, 63].

HO— C«H3
0( >C0\

H0-C«H3 ..

CeH.CO

(Inner anhydride of resorcinplithalein.)

Fluorescein is obtained by heating an intimate mixture of two
molecules resorcin with one molecule phthalic anhydride to 190°-
200°. The materials used in the manufacture should be as pure
as possible, as impure fluorescein is difficult to purify. In the pure
state it forms dark yellow crystals, sparingly soluble in alcohol,
more easily in glacial acetic acid. It is almost entirely insoluble
in water, but dissolves in alkalies, forming a yellowish-red solution,
which, when dilute, exhibits a bright green fluorescence. Acids
precipitate it from the alkaline solution as a yellow powder.

Corresponding chlorofluoresceins are obtained by action of di-
and tetra-chlorophthalic anhydride on resorcin. These com-
pounds are entirely different from thbse formed by direct chlori-
nation of fluorescein. In these the chlorine (bromine, or iodine)
always enters the resorcin-rest. The fluoresceins from the
chlorinated phthalic acids serve as starting-points for a series of
very brilliant phthalei'n dyestuffs, which were first introduced into
the colour-industry by E. Noelting.

The chlorinated fluoresceins have a somewhat redder shade
than the corresponding fluoresceins which contain no chlorine.

Eosin. .

On treating fluorescein with bromine, substitution of the
hydrogen atoms in the resorcin-rests takes place. The final
result is that four hydrogen atoms of the fluorescein are replaced
by bromine, the product being tetrabromfluorescein, C2oH805Br4
[63].

The latter, and also the lower brominated products are beau-
tiful red dyestuffs, the shade being yellower with less, and bluer
with more, bromine. Pure tetrabromfluorescein [63] crystallises
from alcohol in yellowish-red crystals, containing alcohol. It is
almost insoluble in water, but forms easily soluble salts with
alkalies, which exhibit a beautiful green fluorescence in solution.

140 CHEMISTRY OF ORGANIC DYESTUFFS.

From' the alkaline solution, acids precipitate the colour-acid
as a yellowish-red precipitate. The salts are only incompletely
decomposed by acetic acid.

The lead, zinc, alumina, &c., salts are finely coloured insoluble
lakes.

Tetrabromfluorescein and the lower brominated products come
into commerce as sodium or potassium salts, and form the various
brands of soluble eosins.

On wool and silk they are dyed from a slightly acid bath and
produce brilliant shades of red. Those on silk are noteworthy for
their peculiar yellowish-red fluorescence.

Two of the four bromine atoms are contained in each resorcin
group, and on melting with potash eosin splits up into phthalic
acid and dibromresorcin [64]. The bromine may be removed
by nascent hydrogen ; on reduction with sodium amalgam colour-
less fluorescin, C20H14O5, is formed, and yields fluorescein on
oxidation. Various methods have been proposed for the bromina-
tion of fluorescein on a large scale. For example, an alkaline
fluorescein solution is mixed with the calculated amoiint of
bromine dissolved in alkali, and on adding acid the fluorescein
and bromine are liberated simultaneously and combination is thus
effected. This process does not, however, appear to be successful,
and at present bromination is carried out in alcoholic solution.
Fluorescein in a finely divided state is suspended in alcohol, and
the requisite amount of bromine added, the mixture being care-
fully cooled. The hydrobromic acid developed during the
reaction is utilised by addition of potassium chlorate, which again
liberates the bromine. In this manner a saving of bromine is
effected, and only four atoms are necessary, while under ordinary
conditions eight atoms are required, four being lost as hydro-
bromic acid.

Ethers of Eosins [63].

By treating the potassium salt of eosin with methyl iodide or
chloride, or with ethyl bromide, monomethyl- and monoethyl-
ethers of eosin may be obtained, and these even surpass the eosins
in brilliancy of shade, their tone being in general somewhat bluer.

They are monobasic acids, as one unaltered hydroxyl group is
present. The salts are insoluble in water and absolute alcohol,
but dissolve with tolerable ease in alcohol of 50 per cent. The
solutions show a magnificent fluorescence.

TRIPHENYLMETHANE DYESTUFFS. 141

The potassium salt of monoethyltetrabromfluorescein,
r TT O /^sHs

forms large ruby-red crystals with a fine green reflex.

The ethyl ether, in form of its sodium or potassium salt, is
extensively used in silk-dyeing as spirit eosin or '' primerose h
Falcool/' For use, the commercial product is dissolved in
spirit and gradually added to the dye-bath, which is acidified with
acetic acid.

Colourless ethers of eosin also exist, and may be prepared by
heating the silver salt of eosin with alcoholic iodides [63] .

Iodine Derivatives of Fluorescein.

The commercial products known as " erythrosin ^' are iodine
derivatives of fluorescein corresponding to eosins. The alkali-
salts, which are the commercial products, are soluble in water, and
possess a much bluer tone than the corresponding eosins, and
their solutions do not exhibit the fluorescence characteristic of
the latter bodies.

The commercial brands of erythrosin are of various marks,
according to the amount of iodine they contain. On cotton they
may be fixed in form of an insoluble alumina lake, and on this
account are used somewhat extensively in cotton-dyeing, and also
to a certain extent in colouring paper.

Dinitrodihromfluorescein,
C2oH8Br2(N02)205 [62].

This dyestuff is formed by bromination of dinitrofluorescein or
by nitration of di- or tetrabromfluorescei'n. On a large scale it
is prepared by treating dibromfluorescein with nitric acid in
alcoholic solution. Pure dinitrodibromfluorescei'n forms yellow
needles, sparingly soluble in alcohol and acetic acid. It is a
strong dibasic acid, and forms easily soluble salts with alkalies.
The solutions of its salts are yellow if concentrated, red if dilute,
and do not fluoresce.

The sodium salt is known in commerce as Eosin Scarlet,
Safrosin, or Lutecienne.

142 CHEMISTRY OF ORGANIC DYESTUFFS.

It produces a beautiful bluish-red shade on wool^ and may be
used in conjunction with yellow dyestuffs^ giving fine scarlet
tones. Its application in wool-dyeing has fallen off considerably
since the introduction of the red azo-dyes.

Tetrahromdichlorfluorescein.
C^oHeCl^BrA.

Tetrahromtetrachlorfluorescem.
C2oH4Cl4Br4b,.

These bodies are prepared in a similar manner to the cosines,
by bromination of the di- and tetra-chlorfluorescein. The soluble
alkali-salts of these acids are brought into commerce as the various
brands of Phloxin.

Their ethyl ethers, which, like those of eosin, are soluble in
dilute alcohol, are known commercially as Cyanosin. Iodine
derivatives of di- and tetra-chlorfluorescein form the principal
constituents of the dyestuff known as Rose Bengal.

The fluorescein derivatives containing chlorine are much bluer
in shade than the corresponding derivatives of ordinary fluorescein.
Their principal application is in silk-dyeing. Rose Bengal pre-
pared from tctrachlorphthalic acid is the bluest of these dyestuffs,
while Phloxin from dichlorphthalic acid is the yellowest.

Here again the shade may be varied at will by introduction of
more or less iodine or bromine.

Bhodamine [75].

The phthalei'ns of metamidophenol and its derivatives have been
introduced into commerce under the above name. These dye-
stuffs are characterised by the brilliancy of the shades which they
are capable of producing, in fact excelling in beauty all other red
dyestuffs.

Commercial rhodamine consists principally of the phthalein of
diethylmetamidophenol. The condensation of metamidophenol
(and its derivatives) with phthalic anhydride only takes place in
presence of strong sulphuric acid.

Rhodamines may also be prepared by action of dimethyl- or
diethylamine on the chloride formed on treating fluorescein with
phosphorus oxychloride.

TRIPHENYLMETHANE DYESTUFFS. 143

The constitution of the simplest rhodamine is probably
analogous to that of fluorescein, and is expressed by the
formula : —

o< >c<' \co.

Unlike the ordinary phthaleins, rhodamine possesses basic and
acid properties. It forms soluble salts, from which the base is
not separated by alkalies. The solutions are turned yellow by an
excess of mineral acid.

The shade of rhodamine is a magnificent red, and exhibits on
silk a hitherto unrivalled fluorescence.

More recently the condensation-product of succinic acid and
dimethylmetamidophenol has been prepared on a large scale and
sold as E/hodamine S. It is especially adapted for cotton-dyeing.

Pyronines [76].

The Pyronines are a series of red basic dyestuff*s of comparatively
recent introduction. They are derivatives of diphenylmethane,
and resemble the rhodamines in shade. A typical pyronine may be
prepared as follows : — Dim etliylmet amid oplienol is condensed
with formaldehyde, and the resulting dioxytetramethyldiamido-
diphenylmethane is treated with strong sulphuric acid, whereby
one molecule of water is split off", and a leuco-base, tetramethyl-
diamidodiphenylmethane-oxide, is formed, according to the equa-
tion : —

/N(CH3),

CeH3<0H CeH3-N(CH3)2

^6^3\N(CH3)2

CH^ „„ =H20 + CH,< >0

C«H3<i^!iT. , CeH3-N(CH3)2.

From this the dyestuflf (Pyronine G) is obtained by oxidation.
It has the formula : —

CeH3-N(CH3)2
CH/ >0

CcH3— N(CH3)2C1.

Pyronine B is the corresponding ethyl derivative.
The pyronines yield brilliant bluish-red shades on cotton
mordanted with tannic acid.

144 ^ CHEMISTRY OF ORGANIC DYESTUFFS.

Galle'in and Ccerule'in [65].

Galle'in. — The first product of the interaction of phthalic
anhydride and pyrogallol is a phthalein anhydride analogous to
fluorescein, which_, however, undergoes further oxidation by the
air, two hydroxyl groups being converted to quinone groups. Tlie
galle'in thus formed possesses the formula —

HO
O CgH^ CeH^

O/ V<^ yCO.

O \l{, o

It dififers from fluorescein in containing two quinone oxygen
atoms in combination with two benzene rings.

Galle'in is generally prepared by heating phthalic anhydride
with gallic acid to 200°. The latter is converted into pyrogallol
at this temperature, carbonic acid being split off".

In the pure state galle'in forms brilliant green crystals or a
brownish-red powder, easily soluble in alcohol with a dark red
colour, and difiicultly soluble in ether.

The salts with the alkalies, lime, and baryta are soluble in
water with a red colour, which is turned blue by an excess of
alkali. On reduction, it is converted to hydrogalle'i'n and, finally,
to gallin. It forms greyish-violet lakes with alumina and
chromic oxide. It produces a fine violet on wool mordanted with
bichromate.

In printing it is applied with acetate of aluminium or chromium
and steamed, whereby acetic acid is liberated, and the aluminium
or chromium lake of galle'in is fixed on the fibre.

Ccerule'in [65], CsoHgOe, is formed by heating galle'in with
twenty times its weight of concentrated sulphuric acid to 200°.
The dyestuff' is precipitated by water, and in this state forms a
bluish-black powder, which takes a metallic lustre on rubbing.
It is almost insoluble in water, alcohol, and ether, slightly soluble
in glacial acetic acid with a green colour, and easily in concen-
trated sulphuric acid with an olive-green colour. It forms a blue
solution with hot aniline.

TRIPHENYLMETHANE DYESTUFFS. 1 15

It crystallises from hot concentrated sulphuric acid in warty
crystals. Reducing-agents convert it to reddish-brown coerulin,
C2oH]206- On warming with acetic anhydride^ a triacctylccerulein,
C2oHi)Os(C2H30)3, is formed. Ccerulem forms colourless soluble
compounds with bisulphites; these compounds being easily
decomposed by boiling or by action of alkalies or acids. In
dyeing and printing the bisulphite compound is generally used.
For printing, the coerule'in bisulphite compound (CoeruleTn S) is
mixed with aluminium or chromium acetate, printed^ and steamed.
This decomposes the acetate and the bisulphite compound simul-
taneously, and coerulein becomes fixed as aluminium or chromium
lake. Wool is previously mordanted with bichromate and tartar.

The shades produced are dark green^ not very bright^ but
useful on account of their great fastness.

On distilling with zinc powder, coerulein gives phenylanthra-
cene, and, according to Buchka, is a derivative of phenyloxan-

thranol : —

OH ,
I

The constitution of coerulein is expressed by the following
formula : —

CO OH

CeH,^ >C«Hv O

")c/ O I [66].

-O

O— ^CeH^"—

Glycereins [67].

Reichl gives this name to a series of coloured products obtained
by action of phenols on glycerin in presence of concentrated
sulphuric acid. The quantity of dyestuft" formed is, however,
so small that one can scarcely formulate any reaction in form
of an equation.

Similar bodies to these from glycerin are also obtained from
many organic acids, alcohols, and sugars.

146

CHEMISTRY OF ORGANIC DYESTUFFS.

CHAPTER VI.

QUINONEIMIDE DYESTUFFS.

The dyestuffs comprised under this head are derivatives of the
hitherto unknown imido-compounds of the quiuones, and include,
amongst others, the Indamines and Indophenols.

By replacing the oxygen atoms of quiuone by the divalent
group NH, the following compounds are obtained, according as the
substitution takes place once or twice.

and

These compounds are unknown in the free state. Various
derivatives are, however, known, amongst the simplest of which
may be mentioned quinonechlorimide and quinonedichlordiimide.

NCI

Quinoneclilorimide.

NCI
Quinonedichlordiimide.

QUINONEIMIDE DYESTUFF3. 1 17

The above-mentioned indamines and indophenols must be
regarded as more complex derivatives of the quinoncimides.

These dyestuffs are formed by oxidation of a paradiamine in
presence of a monamine or a phenol, or by action of quinonedi-
chlordiimide on the latter.

In the oxidation process, as, for example, that of parapheny-
lenediamiue Avith aniline, the former is probably converted into
quinonediimide HN^=C6Hj^==NH, which, on further oxidation
attacks the benzene chain of the aniline, and enters in the para
position to the amido-group. The indaraine produced has the
constitution [1] :

NH NIL

This constitutional formula is deduced from the followinsr
facts : — On reduction the compound takes up two atoms of
hydrogen, forming paradiamidodiphenylamine : —

H2N— CfiH,— N H— CeH,— NH2.

As the indamine may be reproduced on oxidation, this body
must be regarded as the leuco-base of the dyestuff. That the
nitrogen atom effecting the linkage in the indamine is tertiary
is seen from the fact that a paradiamine substituted in both
amido-groups, as, for example, diethylparaphenylenediamine,

C2H5— HN— CeH,— NH-C2H5,

is incapable of forming an indamine. That the nitrogen atom
effecting the linkage in the indamines occupies the para position to
the amido-group is easily proved, as paradiamines do not react with
para substituted monamines, or at least only in a different manner.
Para-diamines substituted in one amido-group react like primary
amines, and the monamine may also be secondary or tertiary. In
many such cases the formation of an ammonium-chloride group

148

CHEMISTRY OF ORGANIC DYESTUFFS.

(=N(CH3)2)
has to be assumed.

The behaviour of certain tertiary indamines shows that their
production is attended by an intermediate formation ofaquinone-
imide. If, on the one hand, paraplienylenediamine is oxidised
with dimethylaniline, and, on the other, unsymmetrical dimethyl-
paraphenylenediamine [(CH3)2NC6H4NHo] with aniline, indamines
are formed in both cases, but are not identical v.dth each other,
but- isomeric, as by further action of aniline they yield two
different dimetliylsaffranines.

This behaviour is easily explained under the following
assumptions ; — Paraphenylenediamine yields first the body
HN — CeH4 — NH; while from dimethylphenylenediarainc the
chlormcthylate, Cl(CIl3)2N — CeH^ — NH, is produced. The
further action of these compounds on the respective monamines
must necessarily produce dift'erent indamines, the constitution of
which is exjjresscd by the following formulae : —

i\(CH3),

II CI

N(C[r3)

NH.,

It is not improbable that the red dyestuff obtained by Wurster
by oxidation of dimethylparaphenylenediamine is none other than
the chlormcthylate of methylquinoneimide : —

Cl(CH3)2=N=CeH,NH.

This compound yields dimethylpheuylenediamine on reduction,
and reacts with monamines and phenols to produce indamines
and indophenols.

The indophenols are related to the analogues of oxyamidodi-
phenylamine in the same manner as the indamines are todiamido-
diphenylamine.

QUINONEIMIDE DYESTUFFS. 1 19

The formation of dyestufts by oxidation of paradiamines with
nionamines was first discovered ])y R. Nietzki [48] in 1879, who
hiter [1] determined the constitution of the indamines. Witt,
in 1879, discovered the reaction between nitrosodimethylaniline
and amines and plienols.

Bernthsen [36] showed later that certain dyestufts containing
sulphur (methylene blue and Lauth's violet) also belong to this
class of colouring- matters.

1. INDAMINES.

Indamine (Phenylene Blue) [1].]

H,N— CgH,.

^N.
HN=C«H4^

This compound is formed by oxidation of p-diaraidodiphenyl-
amine, or of a mixture of equal molecules of paraphenylenediamine
and aniline. It is the simplest member of the indamine series,
and its salts are greenish blue and are mostly soluble in water.
Acids turn the solutions green, and rapid decomposition, with
formation of quinoue, sets in. The iodide separates in long
brilliant green crystals from a mixture of the hydrochloride and
potassium iodide. Indamine, on reduction, yields paradiamido-
diphenylamine. On heating with a solution of an aniline-salt,
phenosaffranine is formed.

Tetramethylindamine [1, 2, 3].

(Bindschedler's Greex.)

(CH3)2N-CeH,^

(CH3),=N=CeH,^

/
CI

This compound is obtained by oxidation of equal molecules of
dimethylparaphenylenediamine and dimethylaniline [1, 2, 3].
The solutions of the salts have a fine green colour, which is turned

150 CHEMISTRY OF ORGANIC DYESTUFFS.

blue by alkalies. If the action of the latter is protracted, dimetbyl-
amine is evolved^ and probably an indophenol

is formed. This indamine is in general more stable than the
former one, but is decomposed on warming with acids, quinone
and dimethylaniline being formed.

It yields tetramethyldiamidodiphenylamine [1] on reduction.

Iodide, CicH2olSr3l [1], is formed on addition of potassium
iodide to a solution of the hydrochloride or zinc double salt, and
separates in long green needles. It is pretty soluble in pure
water, but insoluble in a solution of potassium iodide.

Zinc double salt [2, 3], (Ci6HooN3Cl)2,ZnCl2, forms coppery
needles, which are easily soluble in water.

Mercury double salt, (C,6H2oN3Cl)2,HgCl2.

Platinum double salt, Ci6H2oN3Cl2,PtCl4.

Tohiylene Blue [1, 4].

I
(CH3)2=NCeH5

Tohiylene blue may be obtained by mixing solutions of
equivalent quantities of nitrosodimethylaniline hydrochloride and
metatoluylenediamine, and also by oxidation of the latter base
with dimethylparaphenylenediamine. It is an amido-indamine
characterised by a greater degree of stability than the previous
ones. The monoacid salts are blue, and the diacid salts are
colourless.

The hydrochloride, CigHi2N4,HCl, forms soluble needles which
possess a coppery lustre.

On reduction, toluylene blue gives triamidotolylphenylamine.
On heating, toluylene red [4] {see Azine Dyestuffs) is formed.

The red dyestufF obtained by Wurster by oxidation of dimethyl-
paraphenylenediamine is probably closely related to the inda-
mines [5]. According to Wurster and Sendtuer, this compound

QUINOXEIMIDE DYESTUFFS.

151

corresponds to a base of the formula CgIIioN2. It possesses the
remai'kablc property of reacting with amines and phenols to pro-
duce indamines and indophenols respectively. It is possible that
this compound is a methylate of methylquinone-diimide of the
constitution —

Tetramethylparaphenylenediamine gives a blue dyestuff,
CioHi4N2^ on oxidation.

2. INDOPHENOLS [7, 8, 12].

This series of dyestuffs, which were first prepared by Witt and
Koechlin, by simultaneous oxidation of paradiamines or para-
amido phenols with phenols, exhibit, both as regards constitution
and general behaviour, a close relationship to the indamines.
Like the latter, they are decomposed by acids with formation of a
quinone. In general they possess a weak basic nature, but,
unlike the indamines, form colourless salts, and have mostly a blue
or violet colour in the free state.

On reduction they yield analogues of paramido-oxydiphenyl-
amine.

Indophenols may be obtained by oxidation of paradiamines with
phenols, or by action of nitrosodimethylaniline or quinonechlor-
imide on the latter class of compounds.

According to the above remarks the constitution of the simplest
indophenol (from paraphenylenediamine and phenol) should be
expressed by the formula,

HN=C6H4=N— CJI^—OH ;

but the properties of the compounds of this class agree better
with the formula —

0=C,H4=-N— C,H,— NH2.

For example, the indophenols do not possess acid, properties,
as might be expected if an hydjoxyl group were present; on the
contrary, they are weak bases.

The leuco-compounds, however, possess decided phenolic pro-
perties. They are soluble in alkalies, but oxidise extremely

152 CHEMISTRY OF ORGANIC BYESTUFFS.

readily in the air, iiidophenols being formed, wliich, being
insoluble in alkalies, separate out. In presence of acid the leuco-
indophenols are stable in the air.

The application of these dyestuffs in dyeing and printing is
based on the above properties of the leuco-compounds. The
process is similar to indigo vat-dyeing. The goods are impreg-
nated with an alkaline solution of the leuco-compound, the colour
being developed by oxidation in the air, or by passing through a
bath of potassium bichromate. Indophenol may also be produced
directly on the fibre, a mixture of the diamine and phenol being
applied, and the dyestufF developed by passing through bichromate
or bleaching-powder solution.

Only the indophenols from dimethylparaphenylenediamine and
a-naphthol and phenol have been found capable of technical
application.

The former compound is of an indigo-blue colour, and
crystallises from benzene in brilliant green needles. It forms a
colourless solution with acids ; an excess decomposes it with
formation of a-naphthaquinone and dimethylparaphenylene-
diamine [12]. The dyestuff from phenol is greenish blue.

The manufacture of the indophenols is effected by oxidation of
an alkaline solution of the reacting compounds with sodium hypo-
chlorite, or with air in presence of copper oxide. An interesting
method of obtaining indophenol is by the action of dibrom-a-
naphthol on dimethylparaphenylenediamine.

The indophenols are very fast to soap and light ; their great
sensitiveness towards acids and certain difficulties encountered in
their application, however, render them unable to compete with
indigo. Indophenol, however, appears to be of use when combined
with indigo, i.e. when a vat of the mixed dyestuffs is used. It is
claimed that this mixed vat is more economical than thesimpleindigo
vat, Avhile the fastness and beauty of the shades are not affected.

A trichlor indophenol,

(CH3)2N-CeH4

0=CeHCl3^

has been obtained by Schmitt and Andresen [10] by action of
trichlorquinonechlorimide on dimethylaniline. It forms beautiful
green needles.

Dyestuffs may also be produced by action of quinonechlorimide
and of nitrosophenol on phenols in alkaline solution. They are.

QUINONEIMIDE DYESTUFFS. 153

however, very xmstable, and probably contain an liydroxyl group
in place of the amido-group in the previously described indo-
phenols. The simplest of these compounds would possess the
formula :— HOC^H^.

~N.

0=C6H,

3. INDAMINES AND INDOPHENOLS CONTAINING

SULPHUR.

(Thiazines.)

This class comprises a series of dyestuffs corresponding to the

indamines and indophenols, but which contain one atom of sulphur

in their molecule. This sulphur atom effects a linkage between

two benzene rings, and the indamines of this series stand in the

same relationship to thiodiphenylamine,

as the common indamines do to diphenylamine. The sulphur atom
enters the two benzene chains in the ortho position to the imido-
group, and accordingly thiodiphenylamine may be regarded as
containing three rings each containing six members. This is ex-
emplified by the following formula [36]: —

H H

CSC

HC C C CH

I II II I .

HC C C CH

^c^V'c^

H H H

The araido and liydroxyl derivatives of thiodiphenylamine are,
like those of diphenylamine, leueo-compounds.
There is an erroneous impression that the group

Nil

154 CHEMISTRY OF ORGANIC DYESTUFFS.

acts as chromoplior, and that thiodiphenylamine is tlie chromogen
of this class of dyestuffs. From Bernthscn's constitutional for-
mula, however^ these bodies belong to the Indamine group, and
their chromophor must be the paraquinonediimide group —

N—

Nil

This is evident from the fact that the amido derivatives of
thiodiphenylamine are not dyestuffs, l)ut leuco-compounds. The
presence of the sulphur atom serves to give greater stability
to the molecule, and these bodies are stable to acids.

In general, the whole character of the series is considerably
modified.

The simplest indamine,

<
^C6H4=1\H

corresponds to Lauth's Violet :

CeHa-NH,

< >s .

^CeH3=NH

In this series also the nitrogenous groups are generally in the
para position to each other.

The sulphuretted indamines may be produced by introduction of
amido groups into thiodiphenylamine, and oxidation of the result-
ing leuco-compounds. They are generally prepared, however, by
a peculiar reaction discovered by Lauth [14] . If a paradiamine is
oxidised in presence of sulphuretted hydrogen in acid solution,
one atom of nitrogen splits off as ammonia, and two molecules of
the diamine combine, one atom of sulphur entering into both rests
simultaneously. The resulting body is an indamine containing
sulphur. These compounds are also formed on oxidation of thio

QUINONEIAIIDE DYESTUFFS. 155

derivatives of paradiamines. Small quantities are further obtained
by oxidation of amidodiphenylamines in presence of sulphuretted
liydrogen.

These dyestuffs are far more stable than the indamines and
indophcnols, and, unlike these, do not give quinone when treated
with acid. For this reason they are capable of practical applica-
tion, one of them, methylene blue, discovered by Caro, being used
on a very large scale. The dyestuffs of this class have a violet or
blue shade.

Lautlis Violet {Thionine) [14, 36].

/C6H3-N=H.3

^C«H3=NH

is formed by oxidation of paraphenylenediamine hydrochloride
in presence of sulphuretted hydrogen, by fusing paraphenylene-
diamine with sulphur and oxidising the resulting compound, and
finally by oxidation of paradiamidothiodiphenylamine.

The base, C12H9N3S, forms a black crystalline powder or needles
with a greenish reflex. It dissolves in alcohol, forming a reddish-
violet solution, and in ether, forming an orange solution.

Hydrochloride, Ci.2H9N3S,HCl, forms beetle-green needles, so-
luble in water with a violet colour.

Hydriodide, Ci2H9N3S,HI, is sparingly soluble in water [36].

Lauth's Violet gives a green solution with concentrated sulphuric
acid, and. on dilution the colour changes through blue to violet.
On reduction it yields paradiamidothiodiphenylamine [36] .

Isothionine is an isomeric dyestuff formed by oxidation of a
diamidothiodiphenylamine of unknown constitution [36] .

Methylene Blue [13, 15, 16, 36, 53].

/CeH3-N=(CH3)o
N. >S

^CeH3-N=(CH3)3
^Cl

This dyestuff was discovered by Caro, who obtained it by oxida-

156 CHEMlSTllY OF ORGANIC DYESTUFFS.

tion of dimethylparaphenyleuediamiue in presence of sulphuretted
hydrogen.

The dimcthylparaphenylenediamine used in this and other pro-
cesses is prepared by reductionofnitrosodimethylanilinej obtained
by action of nitrous acid on dimethylanihne.

Carols i^rocess was formerly used on an industrial scale. A con-
siderable improvement was effected by oxidising equivalent quan-
tities of dimcthylparaphenylenediamine and dimethylaniline in
presence of thiosulphuric acid. The most recent processes have
for their starting-point dimethylparaphenylenediamine-thiosul-
phonicacid: /^(CH.Oo '[1]

CeHs-S . SO3H [3J

This compound is obtained by oxidation of dimcthylparapheny-
lenediamine in presence of sodium hyposulphite, or by action of
hyposulphurous acid (thiosulphuric acid, H2S2O3) on the red oxi-
dation product of dimethylparaphenylenediamine. Two processes
may be employed for the manufacture of methylene blue from this
compound. (1) The thiosulphonic acid is oxidised with dimethyl-
aniline, whereby an insoluble compound :

r^ „ /N(CH3)3

(CcH,N(CH3)3

tetramethylindamine-thiosulphonate, is formed. On boiling with
zinc-chloride solution, it yields suljdiuric acid and leucometliylene
blue, which is converted into the dyestuff on oxidation. (2) On
reduction, the thiosulphonic acid yields dimcthylparaphenylene-
diamine mercaptan — ~<^/r\rT \ m

A /:n(CH3)2[i]

C6H3-SH [3]

■ ^NHo [4]

or, on treating with acids, the corresponding disulphide (CgHnNgS),.
On oxidation with dimethylaniline, both these compounds give the
same soluble green indamine :

^ ^ /NiCH3)3

|XH,-NiiCH3)2

I I

tetramethylindamine sulphide, which is transformed to leuco-

QUIXONKIMIDE DYESTUFFS. 157

methylene blue and methylene blue on standing or on warming
the solution. Small quantities of methylene blue are formed by
oxidation of tetramethyldiamidodipheuylamine in presence of sul-
phuretted hydrogen, and by treating tetramethyliudamine Avitli
sulphuretted hydrogen.

Another method used in the manufacture of the so-called, ethy-
lene blue consists in treating nitrosodimethylaniline in sulphuric
acid solution (sp. gr. I'i) Avith zinc sulphide. Leuco-methylene
blue is produced, and yields the dyestuff on oxidation.

It is certain that methylene blue is the tetramethyl derivative
of Lauth's violet, although it cannot be obtained by direct methyl-
ation of the latter. Its constitution is analogous to that of tetra-
methyliudamine. Like this, it contains a pentavalent nitrogen
atom, which is in combination with two methyl groups and an
hydroxyl or acid radical. The hydrochloride has the constitution
expressed at the head of the section. The properties of the base
of methylene blue are those of an ammonium base, and this agrees
with the above conception of its c6nstitution. The base is not
easily separated from its salts. It is best obtained by decom-
position of the hydrochloride with silver oxide, and has probably
the formula CigHigNsSOH. It dissolves easily in water with a
blue colour.

Hydrochloride, CielligNgSCl, forms small lustrous leaflets,
easily soluble in water.

Zinc double salt, 2(Ci6Hi8N3SCl) -f-ZuCU + HoO (commercial
methylene blue), forms coppery needles, easily soluble in water,
sparingly soluble in zinc chloride solution.

Hydriodide, CigH^gNsSI, forms lustrous brown needles, sparingly
soluble in water.

Concentrated sulphuric acid dissolves methylene blue with a
green colour. Reducing agents convert it to its leuco-derivative,
tetramethyldiaraidothiodiphenylamine —

/CsH3-N = (CH3)2

NH >S

XH3-N = (CH3)2

This base forms colourless leaflets, which oxidise in the air to
methylene blue. On treating with methyl iodide, the dimethyl-
iodide of peutamethyldiamidothiodiphenylamine —

158 CHEMISTUY OF ORGANIC DYESTUFFS.

/CeH3-N(CH3)2
CH3-N >s

is formed. ^C,ll,-^m,),

As this compound is also formed by methylation of the leuco-
compound of Lauth's violet, the relationship between the two dye-
stuft's is demonstrated.

Like most ammonium bases, methylene blue does not dye wool
easily, but is readily fixed on silk and taniiined cotton. It has
also a slight affinity for un mordanted vegetable fibres. Methylene
blue is principally used in cotton-dyeing. It dyes a greenish
shade of blue, which shows a dull tone similar to that of indigo.
It is very fast to light, and the shades may be readily modified by
other basic dyestuft's, such as methyl violet or malachite-green.

An analogous dyestuff to methylene blue is obtained from mono-
ethylparaphenylencdiamiue [Oehler, 20], and another from meth-
oxydimethylparaphenylenediamiue [Mulhauser, 21].

Imidothiodiphenylimide [36].

n:C >s

"===-C6H3=NH

This body contains one amido group less than Lauth's violet,
and is formed by oxidation of monamidothiodiphenylamine.

The base forms small reddish-brown needles, soluble in alcohol
and ether with the same colour.

Hydrochloride, C^M^'^^^,llC\+l\ll20, forms a brown preci-
pitate insoluble in ether. It dissolves in water with blue-violet
colour, and gives a green solution with concentrated sulphuric
acid. The zinc-chloride, double salt, (C igHsNoSjH CI) gZnClg, forms
long brownish-violet needles.

The compounds hitherto described correspond to the indamines ;
the following ones must be regarded as sulphuretted indophenols,
as oxygen partly takes the place of the nitrogenous groups of the

former.

The influence of the sulphur atom in adding to the stability of
the molecule is also very apparent in these bodies, as they exhibit
a far greater resistance to the action of chemical agents than the
corresponding simple indojphenols.

QUINONEIMIDE DYESTUFFS. 159

Thionoline {Thioxuido][)henol) [36].
N >S

^CeH3=0

This compound may be obtained by oxidation of pararaidoplienol
in presence of sulphuretted hydrogen, or by treating Lauth's violet
with an alkali. In the latter case the imido-group is eliminated
as ammonia.

The base forms yellowish-brown leaflets, with a green reflex ;
the hydrochloride crystallises in fine black needles, forming a
reddish-violet solution with water.

The dimethyl derivative of thionoline (Methylene Violet) is
formed by boiling methylene blue with alkali, methylene azure, the
sulphone of methylene blue, C16H17N3SO2, being simultaneously
produced [36].

The base of dimethyl thionoline, Ci^HioSNsO, forms long needles,
and its alcoholic solution shows a reddish-brown fluorescence.

The hydrochloride crystallises in brilliant green needles which
dissolve in concentrated sulphuric acid with a green colour, and
dyes silk violet.

Oj:ythiodi])henylimi(le [3 6],

N. >S,

^C«H3=0

is produced by oxidation of oxythiodiphenylamine (from oxy-
diphenylamine and sulphur). It forms reddish-brown needles
which dissolve sparingly in ether, acetone, &c., with an orange-red
colour.

Thionol {I)ioxi)thwdi])henylimide) [36],
^CeHsOH

^CeH3=0
is formed, along with thionoline, by boiling Lauth's violet with

160 CHEMISTRY OF ORGANIC DYESTUFFS.

alkali or dilute sulpliuric acid, and also by treating thiodiplienyl-
amine with sulphuric acid containing 75 per cent. SO3. It is
insoluble in water and crystallises from hydrochloric acid in
needles, which contain hydrochloric acid. It possesses simultane-
ously weak basic and strong acid properties.

The acid solutions are reddish violet, the alkaline solutions
violet in colour.

The barium salt, CioHyNSO^BaO, forms brilliant green leaflets
soluble in water.

Methylene Red [19, 36,53].

This compound is a bye-product in the preparation of methylene
blue by the old process. Its formation is greatest in presence of
a large amount of sulphuretted hydrogen.

Its constitution is expressed by the formula

/N(CH3).C1

/ I
CeHs-N

This is deduced from the following properties. On reduction it

/N(CH3)2[4]
yields dimethylparaphenylenediamine-mercaptanCeHg— NH2 [1]

■^SH [2]

and is decolorised by alkalies, the corresponding thiosulphonic

/N(CH3)3
acid, CeHn— NHn , being formed amongst other compounds.
""^S-SOsH
The hydrochloride, CgHgNoSo^HCl, is easily soluble in water,
and is extracted from the solution by phenol. The hydriodide is
more sparingly soluble and crystallises from water in thick prisms.
On reduction, and subsequent oxidation with dimethylaniline,
methylene blue is formed.

QUINONEIMIDE DYESTUFrS. IGl

Methylene Green.

This compound is obtained by treating methylene blue witli
nitrous acid. It dyes textile fibres a fine dark green colour, and
appears, from its properties, to be a nitro-derivative of methylene
blue. In its behaviour towards fibres it resembles the latter.

4. OXYINDAMINES AND OXYINDOPHExVOLS.
(OXAZINES.)

This denomination includes a series of compounds analogous to
the thioindamincs and containing an oxygen atom in place of the
sulphur atom of the latter.

These compounds are formed by the action of nitrosodimethyl-
aniline or of quinonedichlorimide on certain phenols or phenol-
carbonic acids in a hot alcoholic or <. acetic acid solution, or by
oxidation of these phenols with paradiamines at a medium tem-
perature.

The dyestufi^s from /3-naphthol and from gallic acid are best
known. The former was discovered almost simultaneously by
"Witt and Meldola.

Naphthol Blue [29, 51].

C18H15N2O.CI = Cl.N(CH3)2 = CeH3^ >CioHe.

This dyestuff is best prepared by heating nitrosodimethylaniline
hydrochloride with /3-naphthol in alcoholic solution. A part of
the nitrosodimethylaniline becomes reduced to dimethylparapheny-
lenediamine during the reaction.

The base is soluble in benzene with a red colour.

The hydrochloride, Ci8Hi4N20,HCl, and the zinc chloride
double salt form bronzy needles, which form blue-violet solutions
with water.

Platinum double salt, (Ci8HHN30,HCl)oPtCl4.

The compound dyes on cotton prepared with tannic acid, and
produces a somewhat dull violet-blue shade similar to indigo. The
dyestuff is known commercially as Fast Blue, Naphthol Blue, and

162

CHEMISTRY OF ORGANIC DYESTUFFS.

Meldola's Blue. The dyestuflF exerts an extremely irritating action
on the mucous membrane of the nostrils.

/3-naphthol reacts with chlorquinonediimide, producing a red
dyestuff of the composition CieHjoNgO [51]. It does not form a
diazo-compound, and therefore probably contains no free amido-
group. Its constitution is probably expressed by the formula —

The base has a yellow colour without fluorescence, the salts
dissolve in concentrated sulphuric acid with a green colour, which
on dilution turns through blue to red.

Under similar conditions a-naphthol yields a dyestuff which
dissolves in dilute hydrochloric acid with a red colour, and pro-
duces a greyish-violet shade in dyeing.

Resorcin reacts with nitrosodimethylaniline, producing a fluo-
rescent violet dyestuff [29].

Sulphonic acids of this series may also be obtained from
sulphonic acids of the phenols.

Muscarine.

CisHi.N^O.Cl.

This dyestuff is an hydroxyl derivative of naphthol blue, and is
obtained by interaction of nitrosodirdethylaniline hydrochloride
and a dioxynaphthalene, M.P. 186°. Its constitution is repre-
sented by the formula : —

C1N(CH3)AH3< ^CioH^OH.

The base is yellowish brown, and is obtained by precipitating
the violet solution of one of the salts with an alkali. It forms a
bluish-green solution with concentrated sulphuric acid, and on
dilution the colour changes through blue to violet, a violet pre-
cipitate being formed finally. It dyes a dull blue shade on cotton
mordanted with tannic acid.

QUINONEIMIDE DYESTUFFS. 103

Nile Blue.
(C,8Hi«N30),SO,.

This dyestuff is prepared by heating a-naphthylamine hydro-
cliloride with nitrosodimethylraetamidoplienol hydrochloride in
acetic-acid solution to 100°. Nile blue is soluble in water aud
alcohol with a blue colour. Alkalies produce a brownish pre-
cipitate, soluble in ether with a brown fluorescence. Sulphuric
acid dissolves it with a yellow colour, which on dilution changes
through green to blue. On adding hydrochloric acid to an
aqueous solution of Nile blue, the sparingly soluble hydrochloride
is precipitated.

The hydrochloride has the constitution expressed by the formula :

/NX
CI . N(CIl3)2 = CJl3C /C,oH,NH2.

Nile blue dyes on cotton prepai^ed with tannic acid and
tartar emetic, producing a greenish-blue shade of great beauty and
purity, similar to methylene blue, but clearer.

Gallocyanine [32, 51].

This dyestuff has attained considerable importance, especially
in calico-printing, and is obtained by acting with nitrosodime-
thylauiline hydrochloride on gallic acid in a hot alcoholic or
acetic acid solution. The compound crystallises out in brilliant
green needles. The mother-liquors always contain dimethyl-
paraphenylenediamine.

Gallocyanine is sparingly soluble in hot water, alcohol, and
acetic acid. The solutions have a violet colour. It possesses
simultaneously acid aud basic properties, and is precipitated from
the reddish-violet alkaline solution by acids.

Gallocyanine dissolves with difficulty in hydrochloric acid,
forming a reddish-violet solution. Its solution in strong sulphuric
acid is blue.

It forms an almost colourless crystalline compound with sodium
bisulphate.

The composition of gallocyanine is expressed by the formula —

M 2

164 CHEMISTRY OF ORGANIC DYESTUFFS.

and its formation is explained by the following equation : —

SCgHioNsO + 2C7HA = 2C1.5H12NA + C8H12N2 + H2O

Gallocj'anine.

Nitrosodimetliyl-
aniline.

Gallic
acid.

Dimethyl- Water,
paraph enyl-
diamiue.

Gallocyanine is easily soluble in hot aniline, and_, on cooling, an
anilide crystallises in long green needles. This anilide is formed
by action of two molecules of aniline, according to the equation —

CigHi^NoOs + SCJI^NHo = C2,H24N404 + IhO.

This compound may be regarded as an aniline addition-product
of the anilide —

Ci5Hi2NA=NC6H5 [51].

The anilide possesses well-marked basic properties.

The methyl-etherof gallic acid reacts with nitrosodiraethylaniline,
])roducing a methyl-ether of gallocyanine, Cj.^Hn NoOg (CH3) . This
compound is a dyestuff, and is known in commerce as Prune [51].

Prune differs from gallocyanine inasmuch as the former is a
base forming stable soluble salts, while in gallocyanine the acid
properties are predominant.

Nitrosodimethylaniline reacts also with the amide of gallic
acid {" gallaminic acid "), and forms a blue dyestuff, which is met
with in commerce in form of its bisulphite compound under the
name Gallaraine Blue.

Gallocyanine is constituted according to one of the following
formulae : —

HOOC

N(CH3)2

From the fact that the methyl-ether of gallocyanine yields a
diacetyl derivative, the second formula appears the more probable.
The pentatomic nitrogen present is probably saturated by the

QUINONEIMIDE DYESrUPPS. 165

carboxyl group in gallocyanine, or by an hydroxyl group in
Prune, as the base contains no ammonium hydroxyl group.

These three dyestufFs are capable of dyeing on mordants, and
produce violet lakes with iron, aluminium, and especially with
chromium oxides. On account of the fastness of the shades pro-
duced, these dyestuffs are largely used in calico-printing and in
wool-dyeing. In printing, a mixture with sodium bisulphite and
chromium acetate is used, the insoluble chromium-lake being
produced by steaming. Wool may be dyed without any mordant,
but faster shades are obtained by chroming the wool first. Prune
having more pronounced basic properties may be dyed on cotton
prepared with tannic acid and tartar emetic.

Prune comes into the market as a powder; Gallocyanine and
Gallamine Blue generally as pastes.

5. DICHROINES.

Liehermami's Phenol Dyestuffs [30].

As it has been demonstrated that certain of these dyestuflPs are
derivatives of phenoxazine, they are best described here.

On treating phenols in concentrated sulphuric acid solution at
40°-50° C. with nitrous acid, peculiar violet or blue compounds
are formed. They are of distinctly acid character, and are reprc-
cipitated from alkaline solutions on addition of acids. Their
alkaline solutions exhibit a remarkable fluorescence, and for this
reason this class of compounds is also known as Dichroines.

The dyestuff from phenol has the composition, C18H15NO3. It
forms a brown powder, insoluble in water, soluble in alkalies with
a blue colour. The thymol dyestufF has the formula CsoHsgNgO^j
and the orcin dyestuft' C21H18N2O6. Both have a violet colour.

Resorufin ( Weselskijs Biazoresorufin).

C12H7NO3. [31, 33, 34, 54.]

This compound is formed by action of nitro- or nitrosoresorcin
or nitrobenzene on resorcin in presence of concentrated sulphuric
acid at 170°. It may also be obtained from resazurin (see below)
by various methods. Kesazurin yields resorufin on heating alone

166

CHEMISTRY OF ORGANIC DYESTUFFS.

or with concentrated sulphuric acid to 110°, by reduction with
sodium bisulphite, or with zinc powder or iron, and subsequent
oxidation in the air. Resorufin is also formed in the preparation
of resazurin. The following synthetic methods give a clear idea
of its constitution. On dissolving an equal number of molecules
of nitrosoresorcin and resorcin in concentrated sulphuric acid a
(lyestuff is formed, which, on heating the mixture to 100°, goes
over into resorufin. The intermediate product of the reaction
may be regarded as an indophenol of resorcin formed according
to the scheme : —

110

OH II

On heating to 100°, another molecule of water is eliminated,
thus : —

and the resulting resorufin has accordingly the constitution
expressed by the formula —

Oil

Resorufin is also formed by heating nitrosophenol or quinone-
chlorimide with resorcin, or by heating nitrosoresorcin with phenol
or by oxidation of paramidophenol with resorcin, or by oxidation
of asymmetrical amidoresorcin with phenol. These reactions are
all carried out in presence of concentrated sulphuric acid.

Resorufin forms small brown needles, insoluble in water,
sparingly soluble in alcohol and ether, and easily soluble in hot

QUINOXEIMIDE DYESTUFFS. 167

concentrated liydrochloric acid. It dissolves readily in alkalies,
and the solution exhibits a beautiful cinnabar-rcd fluorescence,

Resoriifiii ethijl-ether, Ci2H6N03(C2H5), is formed by heating the
silver salt with ethyl iodide and alcohol. It forms orange-red
needles, M.P. 225°.

Hydroresorufin {Dioxijphenuxazin) : —

HOGeHs^ >t;6H30II.

This is a leuco-compound formed by reduction of resorufin in
acid solution. It forms long silky needles, M.P. 216°. In
alkaline solution it oxidises rapidly to resorufin.

Tetrabromresorvfin is obtained by action of bromine on an
alkaline solution of resorufin. Its sodium salt, Ci3H2Br4N03Na
+ 2HoO, forms the commercial Resorcin Blue or Fluorescent Blue.
It dyes wool and silk in an acid bath, and produces bluish-violet
shades, remarkable for their beautiful red fluorescence.

Besazurin {Weselsky's Diazoresorcin). [31, 33, 34.]
C12H7NO,.

This compound is formed by action of nitrous acid on an
ethereal solution of resorcin. It forms lustrous green prisms,
which are insoluble in water and ether, sparingly soluble in
alcohol, and easily soluble in alkalies. The alkaline solutions
are violet, and have a brown fluorescence.

The constitution of resazurin is not known with certainty. It
contains one oxygen atom more than resorufin, and the two are
evidently closely related from the ease with which resazurin may
be transformed into resorufin. The two also yield the same
dioxyphenazoxiu on reduction. It is probable that resazurin is
expressed by the formula : —

—0-0—
X —

168 CHEMISTRY OF ORGANIC DYESTUFFS.

Acetyl resazurin, Ci2H6N04(C2H30), forms long red needles,
M.P. 222°.

Resazurin ethyl ether, Ci2HeN04(C2H5), forms dark red needles,
M.P. 215°.

Orcimfin. [33,34, 55.]

ChHhNOs.

This compound is formed by action of nitrous acid on an
ethereal orcin solution, and is identical with the dyestuff obtained
by Liebermann by action of nitrous acid on orcin in presence of
sulphuric acid.

Orcirufin yields a monoacetyl derivative, M.P. 204°.

Resorvfamin, CioHgNoOg. — This body is closely related to reso-
rufin, one oxygen atom of the latter being replaced by an amido-
group. It is ol)taiued by heating quinonedichlorimide with
resorcin in alcoholic solution.

Resorufamin is only obtained in small quantity. It is a base
forming salts which are easily soluble, and the solutions exhibit
practically the same fluorescence as the alkaline solution of reso-
rufin.

Orcirufamin, C13H10N2O2, is obtained in a similar manner, but
is formed in larger quantity. It closely resembles the above.

Lacmo'id. — This colouring-matter, which probably belongs to
the above series, was obtained by heating resorcin with sodium
nitrite [46, Traube and Hock]. It forms blue salts with alkalies,
and their solutions are turned red by acids. For this reason it
has been proposed as an indicator in titration.

AZINE DYESTUFFS.

169

CHAPTER VI T.

AZINE DYESTUFFS.

This chapter comprises the saffranines and their allies, amongst
which are the eurhodines, toluylene red, the so-called neutral
dyes, Basle blue, and probably Magdala red and Mauveine.
Most of these dyestulFs have been long known, but we owe most
of our knowledge of their constitution to the researches of
Witt on the eurhodines. Witt observed that a compound of
this class [S7'], obtained by action of a-naphthylamine on ortho-
amidoazotoluene, gives, on removal of the amido-group, tolunaph-
thazine (naphthylene-toluylenequinoxaline). All these dyestuffs
are derivatives of an azine (quinoxaline of Hiusberg). The
simplest body of the azine group is phenazine (azophenylene of
Claus and Rasenack) : —

CgH^.

The group (^ I , which replaces two ortho-hydrogen atoms in

each benzene ring, is the chromophor of the whole series.

The azine group, with the four adjacent carbon atoms, forms a

new ring, containing six atoms, so that phenazine may be regarded

as containing three rings, like anthracene.

n c

Pheuazine.

170

CHEMISTRY OF ORGANIC DYESTUFFS.

The azines are in some respects analogous to the quinone-
anilides.

While in the reaction between a paraquinone and a diamine,
only one amido-group enters into the reaction with one quinone
group, the action of an orthodiamine and an orthoquinone
is just double, both oxygen atoms being eliminated in form of
water with the hydrogen of the amido-group, the nitrogen of the
latter entering in the place of the oxygen.

The reaction wnll be easily understood from the following
graphic equation : —

1
Ha

R-

-N

R + H,0.

The simplest azines are not dyestuffs, they are slightly coloured
bodies, generally yellow, and possessing weak basic properties,
their salts being decomposed by water.

The introduction of amido-groups intensifies the basic character
of the azine, and increases the dyeing properties.

Hydroxyl groups produce colouring-matters of a slightly acid
nature, which have, however, only little tinctorial power.

Monamidoazines (Eurhodines) are only weak dyestuffs, the
dyeing-power being fully developed by introduction of two or
more amido-groups.

The azines are closely related to the indamines ; the latter
being derivatives of paraquinonediimide, while the former corre-
spond to the orthoquinonediimides, only in this case the conden-
sation so common in the ortho series takes place.

The relationship between the two classes of compounds is shown
by the fact that the indamines may be easily converted into
azines, and that monamines, with a free para position capable of
yielding indamines on oxidation, give azines when the para
positions are occupied. The conversion of indamines into azines
is especially instructive in the case of amidoindamines — for

AZINE DYESTUFFS.

example, Toluylene blue. On heating an aqueous solution of
this compound for some time, Toluylene red, an amidoazine, is
formed with elimination of hydrogen. The hydrogen is not
liberated as such, but converts a portion of the toluylene blue to
its leuco-base [4] .

The reaction will be readily understood from the following
equation : —

CIIa).X

-CII.

+ 11,0

NH,

Toluylene blue.

Toluylene red.

The amido-group adjacent to the nitrogen atom linking the
benzene chains in the indamine, loses its hydrogen atoms, and
becomes linked to the second benzene chain, while the imido-
group is simultaneously reduced to an amido-group.

If an oxidising agent is present, the conversion of toluylene
blue into leuco-base does not take place.

The simpler indamines only yield azines in presence of a
primary amine. In this case saflFranines are formed. These
bodies contain probably a phenylazonium group, viz., an azine
group containing a pentatoraic nitrogen atom, which is linked
with chlorine and a benzene ring.

Although the basic character of the azines is increased by the
introduction of amido-groups, the azine group plays the principal
part in the formation of salts. If acetyl groups are introduced
into the amido-groups the basic properties of the compound are
decreased, but not entirely destroyed.

A farther confirmation of this is seen in the behaviour of the
polyacid salts and of the corresponding diazo-compounds.

Diamidoazines generally form three series of salts, of which the
monoacid are red, the diacid blue, and the triacid green. Tlie
two latter compounds are decomposed by water, the first one is
stable.

If a diazo-group is introduced into a diamidoazine the com-
pound forms stalde diacid salts, which have likewise a blue colour.
With a second diazo-group a stable green salt may be obtained.

172 CHEMISTRY OF ORGANIC DYESTUFFS.

As diazo-groups can only be formed from amido-gvoups, and as
the conversion into diazo-compound increases the stable salt-
forming capacity once for each diazo-group, it is a necessary con-
clusion that the acid radical present in the red stable salt cannot
be connected with the amido-groups.

Another point in this connection is that the amidoazines dye
fibres the colour of the monoacid, and not of the polyacid salts,
thus showing that the azine group effects the combination with
the fibre.

In the mon amidoazines both nitrogen atoms appear capable of
combining with acids, at least this is probable from the various
colour-reactions which these bodies give with strong acids.

The azine dyestuffs mostly possess a well-marked fluorescence ;
this appears in some cases in the alcoholic solutions of the salts,
and in others in the ethereal solution of the base.

1. EURHODINES [37,38].

(AMIDOAZIIfES.)

This class of bodies was discovered by Witt. They are formed
by action of orthoamidoazo-compounds on monamines (ortho-
amidoazotoluene on a-naphthylamine), by action of orthoquinones
on triamines with two adjacent amido-groups, and by action of
nitrosodimethylaniline or of quinonedichlordiimide on certain
monamines, in which the para position is occupied [50, 52] .

The eurhodines are in general weak basic dyestutfs. The base
is usually yellow, the monoacid salts red, and the diacid salts
green. Both are readily decomposed by water. The monoacid
salts dye silk red, but on washing a change to the yellow colour of
the base takes place. Most eurhodines give a red solution with
concentrated sulphuric acid, the colour changing through black
and green into red again on dilution. The ethereal solutions of
the bases exhibit a yellowish-green fluorescence.

Eurhodine,

Ci,Hi3N3 [37].
{Amidotolunaphthazine.)

This compound is obtained by heating orthoamidoazotoluene
with a-iiaphthylamine hydrochloride. The base forms golden-

AZINE DYESTUFFS.

173

yellow needles sparingly soluble in alcohol and ether, easily in
aniline and phenol. It sublimes without decomposition. The
ethereal solution shows a green fluorescence. Concentrated, sul-
phuric acid dissolves it with a red colour, which changes through
black and green into red on dilution. It reacts with nitrous acid
producing a diazo-corapound, which is decomposed on boiling
with alcohol^ eurhodol ethyl ether, C17H11N0 — O — CoH.,, being
formed.

The hydrochloride, Ci/HigNgjHCl, forms deep red, bronzy
needles.

Witt accords the following constitution to this eurhodine [28] :

CTT.

-N

NH.,

Eurhodine,
H^N-CeHa^^ i >CioHe [50].

{^Amidophennaphthazine.)

Is formed by action of quinonedichlordiimide on yS-naphthylamine
according to the following equation : —

ClN=CeH,=NCl + CioH7NH2 = C6H

3\ ' )Ci,ne + 2HCl.

NH2

The base has a yellow colour, and fluoresces in ethereal solu-
tion. The salts are red, without fluorescence, and are decomposed

174 CHEMISTRY OF ORGANIC DYESTUFFS.

by water. The compound forms a brown solution with concen-
trated sulphuric acid. It yields naphthophenazine on boiling with
nitrous acid and alcohol : —

C«H.:^ I ^CioHc

I)imethylamido_phennapJithazine,

is prepared by action of nitrosodimethylaniline on /S-naphthyl-
aniline [52].

The base is yellow, dissolves in concentrated sulphuric acid with
a violet colour, and forms blue unstable salts [52].

Amidophenophe7ianthmzine.

This eurhodine is formed by action of phenanthrenequinone on
unsymmetrical triamidobenzene. The base forms yellow flocks
or a brown crystalline powder. The salts are sparingly soluble,
and of a carmine-red colour. The reactions are similar to those
of the preceding compounds [38] .

Eurhodines are also formed by the action of triamidobenzene
on ^-naphthoquinone, glyoxal, benzil, isatine, and leuconic acid.

A dimethyl eurhodine (dimethylamidophenotoluazine),

(CH3)2N-CeH3 = N2=CeH3CH3 [39],
is formed on boiling diazotised toluylene red with alcohol.

AZINE DYESTUFFS. 175

2. EURHODOLS.

(OXYAZINES.)

These bodies are formed by melting the azinesulphonic acids
with caustic potash [40] aud by heating the eurhodines with
concentrated hydrochloric acid to 180° [38].

They resemble the eurhodines in colour and fluorescence, and in
their reactions with concentrated sulphuric acid, but differ in
possessing both phenolic and basic properties.

Oxynaph thotoluazine^

This eurhodol is obtained by heating the corresponding eurho-
dine, C17H13N3, with hydrochloric acid or dilute sulphuric acid.
It dissolves in concentrated sulphuric acid with a red colour, and is
precipitated from this solution in. yellow flocks on addition of
water [38].

EurJiodol,

C24Hi,N20.

[Oooyphenanthi'enenaphthazine.)

This compound is formed by melting phenanthrene-naphthazine-
sulphonic acid (from phenanthrenequinone and a/3-naphthylene-
diaminesulphonic acid) with caustic potash. It dissolves in con-
centrated sulphuric acid with a blue colour, which suddenly
changes into bright red on dilution. Its sulphonic acid is a
yellow dyestuff.

The colour-reactions exhibited by the eurhodols with acids of
different concentrations can only be explained on the assumption
that mono- and diacid salts exist, in which, according to circum-
stances, one or both nitrogen atoms of the azine group exert basic
functions.

3. TOLUYLENE RED.

(CH3)2XC«H3v I >C6H,<' [4].

Toluylene Red is a diamidoazine, the simplest of which, diamido-

176 CHEMISTRY OF ORGANIC DYESTUFFS.

plienazine, is obtained by oxidation of triamidophenylamine with
manganese dioxide.

NH
NH2-C6H3/ ^CeH, . NH,+ O2

nh/

= 2H,0 + NH2-C6H3;; 1 }C,U,-^n,.

Toluylene red is a dimethyl derivative of a homologue of
diamidophenazine, and is prepared by oxidation of dimethylpara-
phenylenediamine with mctatoluylenediamine at the boil, and is
also formed by heating toluylene blue (amidoindamine) [4] (see
introduction to the Azine Dyestuffs) . The base forms orange-red
crystals, which contain four molecules of water. The water may
be expelled at 150°, leaving the anhydrous compound, which is
of a blood-red colour [4J. The alcoholic and ethereal solutions
fluoresce strongly.

The monoacid hydrochloride is a fine red dyestuff, which is
turned blue by hydrochloric acid, and green by concentrated
sulphuric acid. The zinc-chloride double salt forms crystals with
a metallic lustre [4] .

Toluvlene red comes into commerce as Neutral Red, and beinsf a
basic dyestuff is fixed on cotton by means of tannic acid.

Toluylene red contains one free amido-group and yields a diazo-
compound, which gives a dimethyl eurhodine on boiling with
alcohol [39].

By oxidation of paraphenylene-diamine and mctatoluylene-
diamine, a non-methylated toluylene blue is formed which yields
a corresponding toluylene red on heating. This latter forms
a tetrazo-compound which yields methylphenazine (benzene-
tolazine) :

QH4\ ( .CgHgCHa [39],

on boiling with alcohol.

A violet dyestuff, Toluylene Violet, to which Witt ascribes the
formula C14H14N4, is formed by treating toluylene blue with an
excess of mctatoluylenediamine [4] . A similar dyestuff, known
commercially as Neutral Violet, is the product of the oxidation
of dimethylparaphenylenediamine with metaphenylenediamine.

AZINE DYESTUFFS. 177

4. SAFFRANINES [1, 2, 3, 4].

The clyestufFs coming under this classification contain four
nitrogen atoms. Unlike the previous azine dyestuffs^ they contain
at least three hydrocarbon chains. Although their behaviour
shows them to be phenazine derivatives, they differ in many
respects from those previously described. Especially noticeable is
their strong basic character, which in many respects resembles
that of the quaternary ammonium bases, and the characteristic
bitter taste of the latter compounds is also present in the saff'ra-
nines. Another point of diff'erence from the rest of the azine
dyestuffs is that the free base has the same colour as the mono-
acid salts.

The well-marked basic properties of the saff'ranines are doubt-
less functions of the azine group, although two amido-groups are
also present. The hydrogen atoms of the latter may be replaced
by alcohol or acid radicals ; and from the fact that the diacetyl
derivatives are still mono-acid bases, j.t is evident that the strongly
basic properties of the azine group remain unaffected.

The saff'ranines form three series of salts. The mono-acid salts
are, like the base, red and very stable ; the diacid salts are blue,
and the triacid green. The two latter series are decomposed by
water; and in fact the green salts can only exist in presence of
concentrated sulphuric or hydrochloric acids. Both amido-groups
may be diazotised [1]. The primary diazo-compound forms blue
diacid salts, which are formed in slightly acid solutions, and
correspond to the blue diacid saff'ranine salts. The green tetrazo-
compounds have not been analysed, but probably correspond to
the triacid salts. The salts of these diazo-compounds are not
decomposed by water.

The saffranines are products of the following reactions : — By
heating primary monamines with indamiues, whereby part of the
latter undergo reduction [1, 3, 4] ; by oxidation of paradiaraido-
diphenylamine and its analogues with primary bases [1] ; and by
oxidation of paradiamines with two molecules of the latter [3, 4] .

In the oxidation of paradiamines with monamines two different
monamines may be used, of which one only need be primary.
For the diamine and one monamine the same conditions must be
observed as for the production of an indamine, i. e. that the
diamine must only be substituted in one amido-group, and the
monamine must possess a free para position. As an indamine is

178

CHEMISTRY OF ORGAXIC DYESTUFFS.

always formed as an intermediate product, all three processes may-
be said to depend on the same reaction — i. e. an indamine is formed
either from diamidodiphenylamine or from the diamine and one
molecule of monamine. The monamine used in the second stage
of the process must not be substituted in the amido-group, but
the para position need not be free. As, however, certain mona-
miues are not capable of reacting in this sense, as, for example,
ortho substituted monamines such as mesidine and adjacent
metaxylidine do not form saffranine with indamines [41], it may
be conjectured that the monamine not only becomes connected
through its nitrogen atom, but also through an ortho position in
the ring. This assumption receives further confirmation from the
fact that the formula of the simplest saffranine cannot be sym-
metrical, as the amido-groups react differently. Two different
dialkyl saffranines, each substituted in one amido-group, may be
prepared, each yielding a diazo-compound, and tlierefore each
containing one free amido-group.

Numerous formulae have been proposed to express the constitu-
tion of the simplest saffranine in accordance with the above facts;
that of Witt, however, alone fulfils the necessary conditions.
According to Witt the formation of saffranine from the simplest
indamine and aniline proceeds as shown in the following schematic
equation : —

Aniline

hj-droebloiide.

+ 411

^I^L

Phenosaff'ranine hydrocLloride.
Indamine.
According to this assumption the aniline becomes connected
■with the nitrogen atom. of the diphenylamine through its benzene

AZIXE DYESTUFFS. 179

ring, and a derivative of triphenylamine is formed, the indamine
link being dissolved. The nitrogen atom of the aniline simnl-
taneously enters one benzene chain of the indamine, in the ortho
[)osition to the diphenylamine nitrogen atom, and the nitrogen
atoms l)ccome linked and form the azine ring. This saffranine
formula may be shortly written thus : —

N
H2N-CeH3<|>C6H,,

and corresponds completely with the properties of the compound.

Here the amido-groups have different values, and this explains
the isomerism of the alkyl-substitution products. The pentatomic
nitrogen atom, simultaneously linked with chlorine and benzene,
offers distinct reason for the stability of the monoacid saffranine
salts.

Further evidence is afforded by the fact that the saffranine
base contains one molecule of water, and that other plienylazoniuni
compounds have been prepared synthetically.

Witt obtained such a compound by action of phenanthrene-
(juinone on orthoamidophenyl-/3-naphthylamine,

H2N— C.oHe— NH-CJI.,,

and ascribes the following formula to it : —

jHex I /Ci^Hg

;i:

N
'I

The dyestuffs obtained by action of nitrosodimethylaniline
or of quinoncdichlorimide on phenyl-^-naplithylamine are also
probably members of this class of compounds [50, 52] .

The monoacid salts of the saffranine series are generally red ; the
introduction of alcohol radicals into the amido-groups makes the
shade more violet, while the introduction of methoxyl and ethoxyl
groups into the benzene ring tends to produce yellower shades.

The saffranines are dyed on cotton mordanted with tannic acid,
and produce the shade of their monoacid salts. Unmordantcd
cotton is capable of fixing small amounts of saffranine.

The diacid salts are produced by concentrated hydrochloric

180 CHEMISTRY OF ORGANIC DYESTUFFS.

acid and are blue ; the green triacid salts are obtained with con-
centrated sulphuric acid. Both are only capable of existence in
presence of excess of acid, and are decomposed by water with
formation of a monoacid salt. The bases may be obtained by
decomposition of the sulphates with barium hydrate; they are of
the same colour as the monoacid salts, and are easily soluble in
water. They form carbonates with carbonic acid.

The saffranines yield leuco-compounds on reduction, which are
pretty stable in acid solution, but are almost immediately oxidised
to the original dyestuff in presence of alkalies. If the reduction
be effected with acid stannous-chloride solution, one molecule of
saffranine is found to require one molecule of stannous chloride,
showing that two atoms of hydrogen ai'c required for the eon-
version of saffranine into its leuco-base.

Phenosaffranine, by continued boiling with zinc powder and
hydrochloric acid, may be converted into a very stable colourless
base, CigHigNgO.

Besides the reactions already mentioned, saffranines are also
formed by action of amines on amidoazo-compounds [45], by
oxidation of the latter, and by oxidation of the mauveines [28] .
The formation from amidoazo-compounds comes under one of the
general methods, as it doubtless depends on the splitting up of the
azo-compound into a paradiamine and a monamine.

The manufacture of the saffranines is always effected by the
process which depends on the oxidation of one molecule of a
paradiamine with two molecules of a monamine. The bases
necessary are obtained by reduction of amidoazo-compounds.
Orthotoluidine {" Echappes,^'' the recovered oil from Magenta-
manufacture, consisting of orthotoluidine and aniline, may be used)
is submitted to the action of sodium nitrite and hydrochloric acid,
whereby a mixture of amidoazotoluene and orthotoluidine is
obtained ; or, if Echappes are used, a mixture of amidoazotoluene,
amidoazotoluenebenzene, amidoazobenzene, aniline, and ortho-
toluidine is produced. The mixture is then reduced with zinc or
iron and hydrochloric acid, the result in the simplest case being the
production of a mixture of one molecule paratoluylenediamine and
two molecules of orthotoluidine, wliile the principal products from
the mixture of bases are toiuylenediamine and paraphenylenedia-
mine with orthotoluidine and aniline. In any case the mixture is
treated in dilute neutral solution with potassium bichromate and
boiled, or the oxidation may be effected by manganese oxide

AZIXE DYESTUFFS. ISl

(Wclclon mud) in presence of an organic acid. The first product is
an indamine which yields a saffranine on further oxidation Avitli
the monamine. Violet dyestuffs are formed along with the
saffranine, and these, being less basic, may be separated by soda and
chalk, and the saffranine remaining in solution is salted out.
The tolusaffranines are the only ones of importance, and their
chief use is in cotton-dyeing. In conjunction with yellow dye-
stuffs (chrysoidine, auramine, turmeric) they produce shades
similar to Turkey red, but of course inferior as regards fastness.
The saffranines are also used in silk-dyeing and produce beautiful
rose shades.

Plienosajffranine [22, 1, 2, 3].

This compound was first obtained by Witt by the oxidation of
one molecule of paraphenylenediamine with two molecules of
aniline [4]. It may also be obtained by oxidation of equal
molecules of aniline and paradiamidodiphenylamine [1].

The free base may be obtained by decomposing the sulphate
with an exactly equivalent quantity of barium hydrate. On
evaporating the resulting solution in vacuo, the base suddenly
crystallises out in green leaflets, and is then found to have lost its
easy solubility in water.

The composition of the base dried at 100° corresponds to the

formula

C,8HieN,0 = Ci8Hi,N,-fH„0.

At 150° it loses about \ molecule of water.

Saffranine base is not very stable ; it loses ammonia on boiling
with water.

The alcoholic solutions of the base and its salts fluoresce
strongly, while this property is entirely absent in aqueous solutions.

The hydrochloride, C-^^'R-^i^i,)^C\, crystallises from dilute hydro-
chloric acid in brilliant green leaflets, and from water in long
steel-blue needles. Its solution has a fine red colour. It is pre-
cipitated from its solutions by salt and by strong hydrochloric acid.

Nitrate, CigllitN^HNOa, forms green crystals sparingly soluble
in water, and almost insoluble in dilute nitric acid [1, 2].

The sulphate, C1SH14N4H2SO4, forms steel-blue needles.

Platinum double salt [1], (Ci«Hi4N4HCl)2 PtCli, forms lustrous
golden leaflets, insoluble in water.

182 CHEMISTRY OF ORGANIC DYESTUFFS.

Diacetyl-hydrochloride [1], (C18H12N4) (C2H30)2HC1, is ob-
tained by the action of acetic anhydride and sodium acetate on
phenosafl'ranine hydrochloride. It forms lustrous brown leaflets,
and dissolves in alcoholic potash with a violet colour. It is
decomposed on boiling with dilute sulphuric acid, acetic acid and
phenosaftranine being produced.

Diazo-coinjjounds [1].

The diazo chloride,

CisHisN^HCl

^N=NC1,

is formed by action of nitrous acid on the (blue) acid solution of
phenosaflFranine hydrochloride. The solution of the compound is
blue like the diacid satFranine salts, but unlike these does not
change colour on dilution. Its jjlatinmn double salt forms broad
blue needles.

Tlie gold salt, Ci8Hi3N5Cl2(AuCl3)2, forms greenish-grey needles.
On boiling with water two molecules of nitrogen are evolved. On
boiling the diazo-compound with alcohol the base CjsHigNg is
formed (see below) ,

A tetrazo-compound of saffranine may be obtained in solution
by treating the green solution of phenosaffranine in concentrated
sulphuric acid with nitrous acid [1]. The colour of the solution
is not changed on dilution. On boiling with alcohol a violet base,
forming yellow salts, is produced. The chloride of this compound
is probably phenazinephenyl-chloride,

C6H4V,. I ^^^6^i,

/ I
CI CeH,

the mother substance of the safFranines [43]. It is interesting to
note that the colour-reactions of this compound with acids are
exactly the same as those of the acetylated saffranines, from which
it appears that the acetylation has the same effect as the removal
of the amido-groups [43]. The compound in question is more
easily obtained from the base CxgHiglS^a, the intermediate product
in this case being a yellow diazo-compound.

AZINE DYESTUFFS.

183

a-DimethijJphenosaffranine [2],

Ci8HioN'4(CH3)2,

is formed by oxidation of one molecule of dimethylparaphenylene-
diaraiue with two molecules of aniline.

The hijdro chloride, CooHigN^^HCl, is a magenta-red dyestuff
known commercially as Fuchsia.

The nitrate, CooHigN^^HNOs, forms lustrous green needles.

Platinum double salt, {Ci^^ii^J^^^)^'^^^^-

p-Dimethylphenosaffranine [41, 43].

This compound, isomeric with the above, is obtained by oxida-
tion of one molecule of paraphenylenediamine with one molecule
of dimethylaniline and one molecule of aniline. Its nitrate forms
brown leaflets. For the crystallographic comparison of the
nitrates see [43]. ^

Tetramethylphenosaffranine [2].
C:8HioN4(CH3),.

This dyestuff is formed by oxidation of one molecule of di-
methylparaplienylenediamine, one molecule of dimethylaniline,
with one molecule of aniline.

Hydrochloride, CooHooN^.HCl.

Nitrate, C22H22N4,HN03, is a fluorescent dyestutf forming
brownish-violet thick crystals.

Biethylsaffranines [1].

Ci8Hi2N4(C2H5)2.

a. From one molecule of diethylparaphenylenediamine and two
molecules of aniline, and

/3. From equal molecules of paraphenylenediamine, diethyl-
aniline, and aniline.

The hydrochlorides of both modifications form brilliant green
needles, which are violet-red dyestuffs.

The /S-hydrochloride is much more soluble in water than the
a-compound.

Platinum salt, (C22H23N4Cl)2PtCl4.

184 CHEMISTRY OF ORGANIC DYESTUFFS.

Acetyl derivatives [1]. — Both dietliylsafFranines yield basic
monoacetyl derivatives on heating with acetic anhydride and
sodium acetate. The hydrochlorides possess the formula

CoaHssN^Cl.C.HsO,

and form lustrous brown needles, soluble in water and alcohol
with a violet colour. The alcoholic solutions do not fluoresce.

Biazo-compounds.

When treated with nitrous acid the diethylsaffi'anines yield
diazo-compouuds, analogous to the primary diazo-compounds of
phenosaffranine. The solutions have a greenish-blue colour.

The cliloride corresponds to the formula

Co2H2oN3HCl-N=NCl.

Platinum salt, C22H2iN5Cl2PtCl4, forms almost black needles
with a coppery lustre.

The fact that both modifications of dimethyl- and diethyl-
saffranine yield diazo-compounds, gives a certain proof of the
presence of two amido-groups in safEranine.

Two isomeric monoethylsafi'ranines may be obtained in an
analogous manner.

The constitution of the a- and /3-compounds is probably ex-
pressed by the formulae

(CH3)2N-C6H3:; I >6H4.

Q\ \H4NH2

a-Dimetliylsaffranine.

cf 'CeH4N(CH3)2
j3-Dimet]iyisaffr{inine.

(Compare Indamines.)

AZINE DYESTUFFS.

185

Tetraethyl])henosajfranine [1],

is obtained by oxidation of equal molecules of dietliylparapheny-
lenediamine, diethylaniline, and aniline. It forms a zinc chloride
double salt whicli forms beautiful crystals with a golden-yellow
lustre. It is a bluish-violet dyestuff and exhibits a magnificent
fluorescence on silk, but is speedily altered on exposure to light.
It is known in commerce as Amethyst-Violet.

Platinum double salt, (C2GH3oN4,HCl)2PtCl4.

Tetraethylsaffranine does not react with either nitrous acid or
acetic anhydride.

Two dyestuffs, the constitution of which has not been definitely
ascertained, but which from their method of preparation belong
to the saffranine series, are Rubramine and Girofle,

Ruhramine is prepared by acting on orthotoluidine with nitroso-
dimethylaniline in hydrochloric acid solution. It comes into
commerce as greenish-brown powder, and produces a fine red-
violet shade on cotton mordanted with tannic acid.

Girofle, probably a homologue of a-dimethylsafPranine (Fuch-
sia), is obtained by acting on xylidine with nitrosodimethylaniline.
It is used for shading: alizarine violet and reds.

Tolusaffranine [24].

Hydrochloride, CoiHjolS^jHCl, forms fine reddish-brown needles
soluble in water and alcohol.

Platinum double salt, (C2iH2oN4HCl)2PtCl4, forms a yellowish-
red crystalline powder.

The nitrate, CjjiH2uN4,HN03, forms reddish-brown needles
sparingly soluble in cold water.

Picrate, C2iH2oN4CeHo(X02)3, OH, forms reddish-brown needles
insoluble in water and alcohol.

Besides the ortho-compound, formed by oxidation of one mole-
cule of paratoluylenediamine, there exists a second one which is
formed from equal molecules of toluylenediamiue, aniline, and
orthotoluidine, and is distinguished from the former by its lesser
solubility. Both come into commerce as hydrochlorides. The

186 CHEMISTRY OF ORGANIC DYESTUFFS.

latter, if prepared as usual from a mixture of aniline and tolui-
dine, generally contains a lower liomologue, CjoHigN^. These
dyestuffs dift'er but little in shade, and produce on silk, wool, and
cotton prepared with tannic acid, tones about halfway between
magenta and ponceau. Dyestuffs which are to be regarded
as oxymethyl- and oxyethyl-derivatives of phenosaffranine are
produced by oxidation of paraphenylenediamine with two mole-
cules of orthoanisidine or two molecules of orthoamidophenetol.
The orthoanisidine compound has probably the composition : —

Similar bodies are formed if the orthoanisidine is partly replaced
by paranisidine or another j^rimary monamiue. These dyestuffs
are especially characterized by their pure yellow shade. When
dyed on silk they fluoresce strongly, the shades obtained resem-
bling those produced by some of the cosines. Owing to their
high price, however, they have not been used on a large scale.

The compound CigHisNg [43, 49] has already been mentioned
as the product obtained on boiling the primary diazo-compound
of phenosaffranine with alcohol. Its salts have a magenta-red
colour and do not fluoresce in alcoholic solution. Concentrated
sulphuric acid dissolves them with a yellowish-green colour, and
on dilution the colour changes through green to red ; the blue
phase does not occur.

Nitrate, Ci8Hi3N3,HN03, forms brown, difficultly soluble
needles.

Zinc chloride double salt forms lustrous brown needles.

Acetyl derivative, CisHigNsCoHsO, is a violet compound forming
yellow monoacid salts.

The compounds obtained by Witt [52], and by Nietzki and
Otto [50, 51], by action of nitrosodimethylaniline and of quinone-
dichlorimide on plienyl-yS-naphthylamine in all probability belong
to this series.

By action of quinonedichlorimide on phenyl-j8-naphthylamine, a
violet base is produced forming magenta-red salts.

The compound dissolves in concentrated sulphuric acid with a
violet colour which on dilution changes through dirty green into
red. The composition of the salts may be expressed by the
general formula C22H15N3 . R.

AZINE DYESTUFFS.

187

Nitrate, CooHisNs^HNOa, forms fine needles or thicker lustrous
green crystals.

The constitution of the compound is probably expressed by the
formula [50] : —

— ^'IL

The product of the interaction of nitrosodimethylaniline and
phenyl-yS-naphthylamine is a bluish-violet dyestuff, probably a
dimethyl derivative of the former [52] : Neutral Blue.

Nitrosodimethylaniline reacts with paratoluyl-^-naphthylaniine
also, and produces a bluish- violet dyestuff of the composition

From the salts, a red base may be separated, ■which dissolves in
alcohol with an orange-yellow fluorescence.

The compound dissolves in concentrated sulphuric acid with a
red- violet colour, which on dilution changes through green and
blue to violet. The nitrate is very sparingly soluble [52].

Saffranol.
Ci8HioN2(OH)2.

This compound is formed by continued boiling of phenosafPra-
uiiie with baryta water, or alcoholic potash solution. It may be
regarded as phenosaflranine in which both amido-groups are
replaced by hydroxyl. The compound agrees with this assumption
inasmuch as it possesses simultaneously acid and weak basic
properties.

Saftranol forms brass-coloured leaflets, almost insoluble in
iudifl'erent solvents, but easily in ammonia and alkalies with a

188 CHEMISTRY OF ORGANIC DYESTUFFS.

deep carmine-red colour. It is separated from these solutions by
acids, and produces the sparingly soluble salts if an excess be
present.

It forms a red diacetyl-com pound, which yields yellow,
sparingly soluble salts with acids [49].

Indazine M [53]

CI CH

\ /

(CH3)2-N-CeH3(l^\

C34H3oN6Cl2= ^T^^^CgHa,

(CH3),-N-CeH3(|l^/

is produced by action of nitrosodimethylaniline hydrochloride
on diphenylmetaphenylenediamine. It dyes fine blue shades on
cotton prepared with tannic acid.

Basle Blue [54].

C33H2,N,C1= (CHaXNCfiHs^ I ^CioH.N-CsH^CH^

/I
CI C6H4CH3

This dyestuff is obtained by the action of nitrosodimethylaniline
chlorhydrate on the ditolylnaphthylenediamine obtained by heating
a-dioxynaphthalene (M.P. 180°) with paratoluidine and parato-
luidine hydrochloride. The dyestuff forms a brownish crystalline
powder, soluble in water with a bluish-violet colour. It dissolves
in concentrated sulphuric acid with a greenish-blue colour, which
on dilution changes through green to violet, a bluish-violet
precipitate being formed. Basle blue is a basic dyestuff and is
best dyed on cotton prepared with tannic acid and tartar emetic.

AZINE DYESTUFFS. 189

Azine Green [55]

is analogous to the above in constitution, and results from the
action of nitrosodimethylaniline hydrochloride on the diphenyl-
naphtliylenediamine obtained from dioxynaphthylene, M.P. 216°.
It is a basic dyestuff, producing dark green shades which are
pretty fast.

5. MAGDALA. RED.

This dyestuff has been long known_, and was investigated almost
twenty years ago by Hofmaun [27] ; but from the recent researches
of Julius [44] it appeal's that the earlier formula, C30H21N3, is
incorrect, and that its composition is analogous to that of the
saffranines, its formula being C30H20N4. Accordingly Magdala
red may be regarded as a saffranine of the naphthalene series.
Indeed the great stability of the dyestuff, its properties, and the
strong fluorescence of its salts are strong arguments in favour of
this assumption.

Magdala red is obtained by heating a-amidoazonaphthalene Avith
a-naphthylamine hydrochloride in glacial acetic acid solution.
The yield is extremely small. A better yield is claimed in a more
recent modification of the above process, in which a mixture of
the hydrochlorides of a-naphthylaraine and paranaphthylenedia-
mine is heated with amidoazonaphthalene to 130-140° till the
melt has a pure red colour.

Analogous dyestuffs may also be obtained from mixtures of
naphthylenediamine hydrochloride and amidoazobenzene, or with
uaphthylenediamineaniline and amidoazobcnze [56].

Magdala red hydrochloride forms lustrous green needles,
sparingly soluble in water, more easily in alcohol. The salt is not
decomposed by ammonia or caustic soda [27]. The sulphate
forms large green needles [45]. The picrate and platinum double
salt are sparingly soluble in alcohol.

The alcoholic solutions of the salts exhibit a magnificent yellow
fluorescence, which surpasses that of any of the saffranines. The
salts dissolve in concentrated sulphuric acid with a bluish-black
colour.

j\Iagdala red still finds a slight application in special cases in
silk-dyeing, but owing to its enormous price has been almost
entirely superseded by rhodamine.

190 CHEMISTRY OF ORGANIC DYESTUFFS.

6. MAUVEINE [28].
C27H24N4.

Mauveine was the first aniline dyestuff prepared on a large scale
(Perkin, 1856), and is certainly closely related to the saffranine
dyestuffs. Like these, it has strong basic properties, and gives
similar reactions with sulphuric acid. Finally, a saffranine (para-
salfranine, C20H18N4 [28]) is formed by oxidation of mauveine in
acetic acid solution. The fluorescence characteristic of alcoholic
saffranine solution is, however, absent with mauveine.

Free mauveine forms a black crystalline powder, insoluble in
water, soluble in alcohol with bluish-violet colour. It is a strong
base, taking up carbonic acid from the air, and capable of ex-
pelling ammonia from its salts.

It forms three series of salts with acids, and these are exactly
analogous to those of the saft'ranines. The triacid salts are green,
and only obtainable with concentrated sulphuric acid. The
diacids are blue, and, like the former, are decomposed by water.
The raonoacid salts are crystalline, have a reddish-violet colour,
and are stable.

The mauveine salts do not produce their characteristic reddish-
violet colour when dyed on wool, but the shade is the bluer one
of the free base.

Hydrochloride, C27H24N4,IICl, forms small lustrous green
prisms, sparingly soluble in water, easily in alcohol.

Acetate, 02/1124^4,0211402, forms lustrous green prisms.

Carbonate, green prisms with a metallic lustre. Is decomposed
on boiling or drying.

Platinum double salt, (02/1124^4,1101) 2PtOl4, forms large golden
crystals, sparingly soluble in alcohol.

C27H24N4(H01)2PtOl4, dark blue precipitate.

027H24N4,AuOl3, crystalline powder.

Ethyl derivative, 027H23(02Hg)N4, is formed by action of ethyl-
iodide on mauveine in alcoholic solution.

Hydrochloride, 0291128^4,1101, forms a reddish-brown crystalline
powder, sparingly soluble in water, easily in alcohol, forming a
purple solution,

(0291128^4,1101) 2PtOl4, goldcn-grccn precipitate.

Iodide, 029H28N4,HI,l2, golden-green crystals.

AZINE DYESTUFFS. 191

Psendomauveine, C24H01JX4, is obtained by oxidation of pure
aniline, and is very similar to mauveine.

A dyestuff probably identical with psendomauveine has been
obtained synthetically by Fischer and Hepp, by action of para-
nitrosodiphenylamine on aniline hydrochloride [51].

Hydrochloride, C2.jHooiS^4,HCl, green crystals.

Platinum double salt, (Co4HooX4,HCl)2PtCl4.

The mauveine dyestuffs are formed, although only in small
(juantities, by oxidation of primary monamineg in neutral solution
Avith potassium bichromate, cupric cbloridg, lead peroxide, and
other oxidising agents. It has not been determined with certainty
what monamines are capable of yielding dyestuffs of this class ; but
it is probable that the mauveine CorHo^N^is formed from three
molecules of toluidine (ortlio and para ?) and one molecule of
aniline, accordinjr to the equation : —

3C7H9N + CeH;N = C2rHo4N, + lOH.

It is not certain if the violet coloration obtained with bleachine;-
powder and aniline solution is due to. the formation of mauveine,
although this is generally stated.

^lauveine is now of little but historical interest. It was
obtained first by Perkin by oxidation of (impure?) allyltoluidine
with potassium bichromate. It is still manufactured in small
quantities, and used in printing English postage-stamps and for
tinting silk for production of white. At present mauveine salts
are met with in commerce under the designation Rosolane.

A synthetical process for production of a series of saffranine
dyestufts closely related to mauveine is the subject of a recent
patent. It consists in the oxidation of one molecule of para-
midodiphenylamine, or one of its homologues, with two molecules
of aniline, orthotoluidine, or xylidine [58].

The dyestuffs have a violet colour, and in general closelv
resemble the mauveines.

Mauveine may be regarded as a phcnylated saffranine,
C2iHi<jN4(CtjH5). Certainly the violet dyestufts obtained by
action of aniline on safi'ranine are totally different from mauveine,
and apparently belong to the Induline series. The fact that
mauveine cannot be obtained in this manner is, however, no
argument against the assumption that it is a phenylsaftranine, as
all these dyestuffs undergo a complete change in constitution on
boilinjj with aniline.

192 CHEMISTRY OF ORGANIC DYESTUFFS.

CHAPTER VIII.

ANILINE BLACK.

j\losT oxidising agents acting in acid solution produce a peculiar
dyestuff with aniline salts. This body is characterised by its
dark colour, and its sparingly solubility in most solvents. Jts
formation has been observed by the action of the following
agents : — ^langanese dioxide [1] ; lead peroxide, chromic acid [2];
ferric salts [3] ; ferricyanides [3] ; permanganates [5] ; chloric acid
alone [6], or chlorates in presence of certain metallic salts [7],
amongst Avhicli vanadium, cerium, and copper compounds are
the most effective. In all cases these oxidising agents withdraw
hydrogen from the aniline molecule.

The formation of aniline black from chlorates and the above-
• mentioned metallic salts is especially of interest, inasmuch as
very small quantities of the latter suffice for the oxidation of
relatively large quantities of aniline. Vanadium has the most
powerful action in this respect. According to Witz [8], one part
of vanadium, aided by the necessary amount of a chlorate, is
sufficient to convert 270,000 parts of an aniline salt into aniline
black. After vanadium, cerium and copper are the most effective,
iron having considerably less action.

It is evident from this that the metallic compounds act only
as oxygen-carriers. From the fact that only those metals which
form several oxygen or chlorine compounds are capable of pro-
ducing the desired action, it is probable that the higher metallic
oxides effect the oxidation of the aniline, and that these oxides
are continuously regenerated by the chlorate present.

If cupric chloride is applied with an insufficient quantity of
chlorate, it is possible to detect the formation of cuprous chloride

ANILINE BLACK. 193

in the mixture. For the production of aniline black from solu-
tions it is necessary that the latter be acid. The formation of
black, from chlorate and copper salts may, however, take place in
presence of excess of aniline, if the mixture be allowed to dry, as
is the case in black-printing.

The formation of aniline black from chloric acid and aniline
likewise only takes place on drying. Chlorate of aniline is pretty
stable in solution, but if the crystallised salt be dried, it is con-
verted into aniline black, which generally retains the crystalline
form of the chlorate [33]. Finally, aniline black is formed at
the positive pole on the electrolysis of salts of aniline [10, 16].

The substance formed in all these reactions exhibits practically
the same properties. It consists principally of a compound of
weak but distinctly basic character. The base in the free state
has a dark violet, almost black, colour, while its salts are dark
green. The latter are unstable and partly decomposed by water.
It is, however, difficult to remove the whole of the acid by washing.
The base is almost insoluble in most solvents. It dissolves
with difficulty in aniline with a violet colour, which on long
standing changes to brown [11].

It dissolves somewhat more easily in phenol, with a bluish-green
colour. With concentrated sulphuric acid it forms a violet
solution, from which water precipitates the dark green sulphate.
With fuming sulphuric acid it yields sulphonic acids differing
according to the temperature and duration of the reaction. The
sulphonic acids are green in the free state, and form easily
soluble salts with the alkalies. These latter have a violet-black
colour.

The instability of the salts of aniline black renders it difficult
to obtain them with a constant amount of acid. The hydro-
chloride loses hydrochloric acid on drying, and does not form a
definite compound with platinum chloride.

With acetic anhydride, aniline black yields an acetyl derivative,
which possesses little colour, and which is insoluble in concen-
trated sulphuric acid [34].

Methyl and ethyl iodides appear to produce substitution-
derivatives, but differ only slightly from the original compound
[34]. On treating with potassium bichromate, aniline black
gives a violet-black compound, which contains chromic acid and

194 CHEMISTRY OF ORGANIC DYESTUFFS.

appears to be the cliromate of the black base (Chrome-black)
[34]. It is not turned green by acids.

Energetic oxidising agents^ for example chromic acid in a
strongly acid solution, convert aniline black into quinoue [34].
lleducing agents form an insoluble leuco-compound, which
oxidises slowly in presence of acids, and rapidly in presence of
alkalies, aniline black being reproduced.

If the reduction be more energetic, — for example, with tin and
hydrochloric acid, or hydriodic acid and phosphorus, — the black
is completely split up, paraphenylenediamine, paradiamidodiphe-
nylamine [34], and small quantities of diphenylamine being
formed. If the black is submitted to dry distillation, aniline,
paraphenylenediamine, diamidodiphenylamine, and diphenylpara-
phenylenediamiiie are produced [33].

By continued action of aniline on aniline black, products
resembling the indulines are formed. One of these has been
isolated, and is a blue dyestuff of the formula, C36H29N5 or C36H31N5
[18]. •

This substance resembles the indulines, the base having a red
colour in alcoholic or ethereal solution, while the salts are blue.
It probably bears the same relationship to aniline black as the
higher indulines discovered by Witt and Thomas do to the indu-
line C18H1.5N3. (See page 202.)

The numerous analyses made of aniline black show that it is
formed from aniline by simple abstraction of hydrogen. The
values obtained approximate nearly to the simple expression,
CgHsN. Naturally the molecule corresponds to a multiple of
this formula, but the instability of the salts has hitherto rendered
it impossible to determine the molecular formula accurately.

The folloAving formulae have been proposed by investigators in
this direction : —

1. Ci.oHioN^.

2. C18H15N3.

3. C24H00N4.

4. C30H25N5.

No. 1 was proposed by Kayser [12], No. 3 by Goppelsroeder
[15], and Nos. 2 and 4 are due to Nietzki.

Formula No. 4 was based principally on the formation of the
above-named blue dyestuff, which Avas regarded as phenylated

ANILINE BLACK. 195

aniline black, C30H25N5 — CoH.,. Since then, however, Witt [27]
has shown that from the induline CisHioNg clyestufFs may be pro-
duced by the action of aniline, which contain five nitrogen atoms
in the molecule, so that this argument for the formula C30H25N5
becomes useless.

Determinations of the amount of hydrogen required to convert
aniline black into its leuco-corapounds point nearly to two atoms
of hydrogen for the formula C1SH15N3. This appears to be the
correct molecular formula [9] . The fact that the analysis of the
black gives throughout slightly lower values for the hydrogen,
renders it possible that the formula C18H13N3 may be accurate.

Some conclusions as to the constitution of aniline black are
obtained from its decomposition on oxidation and reduction. The
production of quinone in the former, and of paraphenylamine, &e.,
in the latter, render it apparent that the nitrogen atom of one
benzene residue enters the chain of another benzene residue in the
para position to the nitrogen atom. Gc)ppelsroeder's formula [15],
in which the benzene chains are represented as linked in a circle
of imido-groups, corresponds to this view to a certain extent. This
entirely symmetrical formula, however, does not account for the
tinctorial character of the compound in a satisfactory manner ;
and from the formation of a stable leuco- compound it may be
deduced that in all probability at least two nitrogen atoms of the
molecule are linked together.

Liechti and Suida [33] regard the black from aniline chlorate
as a chlorinated product. This is improbable, as on treating
with concentrated sulphuric acid, hydrochloric acid is evolved, and
a sulphate almost free from chlorine is produced.

The adoption of similar processes with orthotoluidine results in
the formation of a compound probably homologous with aniline
black, of the formula C7H7N [34] .

This compound resembles aniline black in all its properties.
The salts arc dark green and the free base is bluish black. The
latter differs from aniline-black base by the fact that it dissolves
in chloroform with a bluish-violet colour [34] .

Paratoluidine does not form an analogous compound on oxidation.

Besides the compound described in detail, aniline black gener-
ally contains others. One of these is the product of a less
energetic oxidation, and is distinguished from the former com-
pound by the brighter green colour of its salts and a brighter violet

196 CHEMISTRY OF ORGANIC DYESTUFFS.

colour of the free base. It also possesses a considerably higher
degree of solubility in alcohol, acetic acid, &c. It dissolves in
concentrated sulphuric acid with a red-violet colour. This sub-
stance is probably the principal constituent of the dyestuff
formerly sold as Emeraldine, and is probably identical with the
product formed by oxidation of paraphenylenediamine with
diphenylamine [17].

An interesting reaction in which eraeraldine is formed was
observed by Caro [16]. If aqueous solution of free aniline is
oxidised with potassium permanganate, and filtered from the
separated manganese dioxide, the filtrate is a yellowish liquid,
from Avliich ether takes up a yellow amorphous compound. This
latter is converted into a green salt of emeraldine by mere contact
with acids. A substance possessing the properties of emeraldine
is formed simultaneously with quinone by oxidation of paramido-
diphenylamine. A larger yield is obtained if this base is oxidised
with an equivalent of aniline, and in this case quinone is not
formed [17]. On further oxidation emeraldine yields a darker
coloured compound, but it is doubtful if this is aniline black. The
formation of emeraldine from paraphenylenediamine and di-
])henylamine leads to the supposition that it is a phenylated
indamine of the formula :

HN=CoH2.

C«H,N-CeII,/

On further oxidation, especially with chlorinating agents, ani-
line black yields a darker product which is no longer turned
green wdth acids.

On boiling the acetate or the hydrochloride of aniline black
with aniline, a mixture of dyestuffs is formed, one of which, a base
of the composition CgeHsgNg, has already been mentioned. The free
base dissolves in ether with magenta-red colour; its salts with
acids are insoluble in water, soluble in alcohol with a blue
colour [18].

CseHggNgjHCl crystallises from alcohol in small needles w^hich
have a coppery lustre.

(C36H29N,,HCl)2PtCl4 forms a violet precipitate sparingly
soluble in alcohol.

CgeHogNg,!!! is similar to the hydrochloride.

C36Ho9N5,C6H2(N02)30H, Sparingly soluble precipitate.

AXILIXE BLACK. l'J7

TECHNICAL ANILINE BLACK.

Aniline black in substance is scarcely ever prepared in tlie
colour manufactory, but is always produced directly on the fibre.
It lias au extended application in calico-printing and cotton-
dyeing, but as yet is of little service in wool-dyeing. For aniline-
black printing innumerable recipes have been published and
patents taken; all depending on one or other of the methods of
formation mentioned in the introduction to this chapter.

The oxidising agent most generally employed is potassium (or
sodium) chlorate in presence of copper salts [7J. As soluble
copper compounds are liable to attack the iron portions of the
printing-machine, copper sulphide [19] is used. On printing,
this is partly converted into copper sulphate, Avhich then enters
into the reaction.

For example, a mixture of aniline hydrochloride, potassium
chlorate, and copper sulpliide, thickened with starch, is printed.
Tiie printed goods are then aged in a moist room, at a temperature
of about 30°, and the oxidation of the sulphide to sulphate and of
the aniline to black takes place.

Vanadium compounds (vanadic acid and vanadium chloride)
have been proposed as substitutes for copper sulphide, but without
much practical success. Potassium ferrocyanide and ferricyanide
are also used to a certain extent. A mixture of these salts with
aniline salt and potassium chlorate is printed, and the goods aged.
The probable action is that the ferricyanide oxidises the aniline,
and is continually regenerated from the ferrocyanide formed by the
chloric acid present. Thus these salts play the part of oxygen
carriers in a similar manner to the copper and vanadium com-
pounds. In the opinion of technologists, the black produced by
this process differs somewhat in its properties from that obtained
with copper, but this may be ascribed to the presence of prussian
blue in the former. In place of the aniline hydrochloride and
potassium chlorate, a mixture of aniline sulphate and barium
chlorate has recently been employed in black-printing.

In printing it is absolutely necessary that the formation of
black should not take place in the liquid mixture, as in this case it
Mould soon become useless. Oxidants, like chromic acid, manga-

198 CHEMISTRY OF ORGAXIC DYESTUFFS,

nese dioxide, &c., which act directly on the aniline, cannot be
employed in printing.

In cotton-dyeing, however, the case is just the opposite, as the
black formation should be as rapid as possible.

For this purpose the formation of black is often effected by the
action between manganese dioxide and aniline salts.

The goods are treated with manganese chloride, and then passed
through an alkaline bath whereby manganous oxide is precipitated
on the fibre. A subsequent oxidation by air or by a bath of
chloride of lime serves to convert this into peroxide, a bottom of
the so-called manganese-bronze being obtained. On passing into
an acid solution of aniline, aniline black is precipitated on the
fibre in a firmly adherent condition.

However, chromic acid is the oxidant generally employed. An
aniline solution containing free sulphuric acid is mixed with a
soluble bichromate, and the goods entered. On heating, the black
is precipitated on the fibre. In all cases the aniline-black salt
formed is converted into the free base by a weak alkaline bath
(soda, soap, or chalk) .

It is merely a matter of conjecture at present if tlie black
produced on the fibre is identical Avith the products examined in
the free state.

The conditions employed in black-printing differ considerably
from those when the compound is prepared in substance; for ex-
ample, the formation of black from aniline salts, chlorates, and
metallic salts only takes place in presence of a considerable excess
of acid. In printing, on the other hand, an excess is avoided,
as it would tend to injure the fibre during the ageing process, and
besides would form the black in the liquid printing-mixture.

For this reason an excess of aniline is generally used, and in
addition a part of the aniline hydrochloride may be replaced bv
the tartrate.

Such a mixture does not form black even on long standing;
this first takes place when the mass has somewhat dried on the
fibre.

In general the oxidation appears to go further than when
working in solution.

The black prepared in substance is converted into dark green
salts by acids, and this property is often a serious drawback to
the black on fibres. This " greening,^^ as it is called, is produced

AXILIxVE BLACK, 199

Oil the goods by acid vapours, for example, by the sulphurous acid
produced by the combustion of coal-gas in work-rooms.

This greening may be avoided or, at any rate, reduced to a
minimum, by energetic oxidation. The compounds produced in
tliis manner are certainly different from the one described, and
are probably its higher oxidation or chlorination products.

Sometimes the goods are submitted to a subsequent treatment
to prevent greening. This may consist in passing through a bath
of bichromate (formation of aniline-black chromate) or of dilute
bleaching-powder.

Aniline black dyed on fibres is one of the fastest colours. It is
stable against soap, is only slightly attacked by light and air, and
is capable of withstanding a slight treatment with chlorine.
More chlorine turns it reddish brown.

200 CHEMISTRY OF ORGANIC DYESTUFFS.

CHAPTER IX.

INDULIXES AND NIGllOSINES.

The dyestuffs included in this classification comprise a series of
colouring-matters produced by action of azo-, nitro-, and nitroso-
compounds on aromatic amines. They comprise a great variety of
shades, from red through blue to almost black.

The indulines are formed ia a great number of reactions.
Nearly all azo-, azoxy-, and amidoazo-compounds, if heated Mith
salts of aniline or other aromatic amines, produce indulines, and
the dyestufl's formed on oxidation of aromatic amines under
certain conditions belong in all probability to this class. It is
difficult to say with certainty to what extent the products of
difi*erent reactions are identical with one another.

The nitroso-derivatives of secondary and tertiary aromatic
amines also react with aniline and its analogues, producing indu-
lines ; and to the study of this reaction and that of the amido-
azobenzene process we owe our present knowledge of the compo-
sition and structure of the indulines. Researches in this direction
have been made by Caro and Dale [21], Martius and Griess [22],
Hofmann and Geyger [23], and Fischer and Hepp [35].

The lower members of the induline series are soluble in water,
the higher ones in alcohol.

The nigrosines comprise that section of these dyestuffs produced
by action of nitro-compounds on aniline hydrochloride in presence
of ferrous chloride. The method employed technically for pro-
duction of indulines consists in heating aniline hydrochloride with
amidoazobenzene. If the reaction be carried out at a low tempe-
rature, and especially if the mixture contains an excess of aniline
hydrochloride, soluble indulines are produced in larger c^uantity.

INDULINES AND NIGROSINES. 201

while with a protracted reaction insoluble indulines, generally of
bluer shadCj are ibrmed.

Induline CigHigNg is formed by heating an amidoazobenzene
melt for 10 minutes at 140°. Another induline, C24H18N4, is also
formed (see below), and is separated by the less solubility of its
acetate in water.

Tiie base, C18H13N3, forms needles with a green metallic lustre,
M.P, 135°; the salts are easily soluble in water and dye reddish-
violet shades.

The indulines are derivatives of phenazine; the simplest has the
constitution : —

CeHs^ >CeH4

) ^N^ =C,8Hi3N3.

NH CeHs

From this the higher indulines are- formed by introduction of
anilido-groups, by phenylation, and by introduction of the rest of
paraphenylenediamine. This latter reaction always takes place in
a normal induline melt, the paraphenylenediamine being formed
from decomposition of amidoazobenzene.

Induline C24Hi8N4 [36] is produced by operating in a manner
similar to above, the temperature of the melt being about 150°.
The melt is extracted with a solution of acetate of soda under
pressure, wdiereby the induline, C24H18N4, goes into solution, and
the free base precipitated by an alkali. The base forms lustrous
leaflets soluble in alcohol with magenta-red colour. The hydro-
chloride forms bronzy crystals soluble in warm water with a
bluish-violet colour. It dyes bluish-violet shades.

^i-fy/zAewme, C30H24N4, is a constant product of the induline melt
and plays an important part, especially in the production of higher
indulines. It is formed also by the action of various nitroso-
compounds on aniline and aniline hydrochloride, the best result
being obtained by paranitrosodiphenylamine. It may be produced
synthetically by action of aniline on dianilidoquinonc. This
synthesis and the production of dianilidoquinonc on heating azo-
phenine with sulphuric acid explains its constitution, which is
that of a dianilidoquinouedianil :

20.2

CHEMISTRY OF ORGANIC DYESTUFFS.

CkHo

N.CeH,
NH . C^ll,
NH.CeH,
N.C«H5

Azophcnine forms red leaflets^ M.P. 240°, wliicli are insoluble
in alcohol and ether, but soluble in aniline, benzene, and toluene
[27, 28]. On heating the melt containing azophenine, other
indulines arc formed, amongst which the following, investigated
by Witt and Thomas, may be mentioned : —

Indulme B, C18H15N3, Azodiphenyl blue.

Induline 3 B, Cs^tLsNg. Tlie hydrochloride is sparingly soluble
in alcohol.

Induline 6 B, CaeHayNj. This is the best characterised of the
induline series. its hydrochloride forms well-detined crystals
which are insoluble in alcohol. Its sulphonic acid dyes wool a
pure blue shade. This induline is probably a phenazine produced
by action of aniline on azophenine according to the equation [37] :

:N.

-NC.Hs CeHsNH.

-NCJls CsH^N ^ ^

According to Wichelhaus and v. Dechend induline B is also
formed by action ot nitrobenzene on aniline hydrochloride, a reac-
tion also observed by Staedeler. An interesting method of obtaining
this body is by heating the aniline salt of phenylamidobenzene-
sulphonic acid (Tropaolin 00). In this case sulphanilic acid
splits oft", Azodiphenyl blue is also obtained by action of azoxy-
benzene on aniline hydrochloride [24] .

According to Wichelhaus and v. Dechend a new colour-base —
Triphenylenediamine, CigHiaNg — is formed on heating the hydro-
chloride of azodiplienyl blue to 230° [24] .

On a large scale the indulines are prepared by heating a mixture
of amidoazobenzene, aniline hydrochloride, and free aniline to the
boiling-point of the latter. Keddish-violet compounds are first
formed which gradually change to blue.

The first products of the reaction are simple soluble indulines
and. azophenine, and from these the higher products are formed by
phenylation. In all probability commercial induline contains a

INDULINES AND NIGROSINES. 203

mixture of dyestuffs. Paraplienylencdijiraine and dipbenylamiiie
are formed as bye-products in the induliue rnelt.

According to Caro a soluble induline is formed by heating
amidoazobcuzene hydrochloride with neutral aniline hydrochloride
to 100° with a little water [29] . This induline may be fixed on
tannined cotton.

An apparently different soluble induline is described by Istel as
being formed on heating 2h parts aniline hydrochloride, 1 part of
amidoazobenzene chloride, and 6 parts of water to 70°-80° C. for
twenty-four hours. The new dyestnff gives a blue solution with
water, and exhibits a reddish-brown fluorescence. It dyes on
tannined cotton, and may be also fixed on unmordanted. cotton
from a bath containing common salt or acetate of soda. The
shades on tannined cotton are very fast to light [38] .

Indulines have also been prepared technically by heating azo-
benzeue with aniline hydrochloride [25] .

Recently a number of patents for the production of soluble
indulines have been published. These are based, for the greater
number on the substitution of a diamine, generally paraphenylene-
diamine, for the aniline in the usual induline melts. A short
summary only of these processes can be given here. The most
important of tiiese consists in heating amidoazobenzene hydro-
chloride with paraphenylenediamine to 180'^ for three or four
hours. A similar product is obtained with amidoazotoluene.
The dyestufPs obtained by this process have found technical appli-
cation, and are known in commerce as Paraphcnylene Blues
[39,40].

Metaphenylenediamine may also be used, but the products are
not so fast to light. Triamidoazobenzenes (Bismark brown) and
Chrysoidine give soluble indulines on heating with paraphenylene-
diamine.

Soluble indulines are also obtained : — (1) By heating spirit-
soluble indulines, azophenine, quinone, chloranil, azobenzene, azo-
toluene, or oxyazobenzene with paradiamines (Poirrier). (2)
By heating diamidoazoxybenzene with aniline and aniline hydro-
chloride. (3) By heating nitro-derivatives of the amines with
aniline &e. in presence of ferrous chloride. (4) By heating the
azo-derivatives of naphthylenediamine [1, 5] with paraphenylene-
diamine and benzoic acid.

204 CHEMISTRY OF ORGANIC DYESTUFFS.

The nigrosines are prepared by heating a mixture o£ nitrobenzene,
aniline, liydrochloric acid, and iron filings to 180°-220'^. The
colour of the mixture changes through reddish violet to deep
blue. They are also prepared by heating a mixture of crude
nitrophcnol (mixture of ortho and para) with aniline hydrochloride
and iron filings. The nigrosines possess a more greyish shade
than the indulines, but it is not known with certainty if the
colouring-matters are different. A series of similar products to
the nigrosines and indulines are formed by oxidation of pure
aniline with arsenic acid, but the exact relationship of these dye-
stuffs one to another is unknown. G. Wolf [31] has published a
series of formula for these bodies, which cannot, however, be
looked upon as trustworthy, as the necessary analytical data are
not given.

The violet dyestuffs of magenta residues differ from the indu-
lines in so far that they give a brown solution with sulphuric acid,
while all the latter give a blue.

Sul phonic acids of the indulines and nigrosines are also known.

The sodium salts of the sulphonic acids of various indulines
come into commerce under the names of Fast Blues, Blackley Blue,
Indigo substitute, &c. The difference of the various marks depends
on the shade of the induline sulphonated and the number of sulpho-
groups introduced.

The indulines are mostly insoluble in water both in form of
bases and salts, but are soluble in alcohol. The solutions of the
bases are red to reddish violet, the salts are bluish violet, blue, or
bluish grey. They are soluble in concentrated sulphuric acid with
a pure blue colour, the sulphu-acids have the same colour as the
salts of the original induline, and the salts of the sulpho-acids have
the same colour as the free bases.

The indulines are destroyed on oxidation, quinone being formed ;
reducing agents produce easily oxidisable leuco-compounds.

The nigrosines have similar properties.

Spirit-soluble indulines and nigrosines are employed as hydro-
chlorides, and are principally used for colouring varnishes. Spirit-
soluble indulines are applied in printing by a peculiar process.
They are printed in combination with tannin and the acetic ethers
of glycerine (monoacetine, diacetine) ; on steaming, these ethers
are decomposed, and the liberated glycerine effects the combination

TNDULINES AND NIGROSINES. 205

of tl»c iiuhiline with the taunin and the tannin lake with the fibre
(Acetiiie blue).

Another process for printing consists in the application of a
mixture of induline and levulinic acid along with tannic acid,
the colour being fixed by steaming [41] .

The soluble (sulphonated) indulines are dyed on cotton mor-
danted with taunin and tartar emetic, a considerable amount of
alum being added to the dye-bath. Wool may be dyed directly
from an acid bath, the induline generally being used in combina-
tion with other acid colours. Silk is dyed in a bath containing
boiled-off liquor, the shades being brightened by addition of sul-
phuric acid.

Soluble indulines of the unsulphonated class are basic dyestuffs,
and are principally used in cotton-dyeing on a mordant of tannic
acid and tartar emetic.

liosindulines [4:2, 43, 44].

These dyestuffs are indulines of the naphthalene and benzene-
naphthalene series.

Xitrosoethyl and nitrosophenylnaphthylamine, if heated with
aniline, produce a deep-red dyestuff, and an analogous compound
is obtained by heating naphthoquinone and certain of its deriva-
tives with aniline and aniline hydrochloride. The latter dyestuff
yields sulphonic acids which dye animal fibres brilliant bluish or
brownish-red shades. The sodium salt of one of these acids is
known as Azocarmine. The rosinduline from nitrosophenyl and
naphthylamine and aniline has the composition CgsHj^Ns. It forms
red monoacid and green diacid suits, the latter are decomposed by
water. Hydrochloride, (CasHiyNonCl)^ + l^HgO, reddish-brown
prisms soluble in water and alcohol. Sulphate, C28H19N3H2SO4-I-
HoO. The constitution of the base may be expressed by the
formula :

206

CHEMISTRY OF ORGANIC DYESTUFFS.

Fluorindines.

These comprise a series of weak dyestuffs discovered by Caro
and Witt, the type of which is obtained by heating azophenine
with concentrated sulphuric acid or with zinc powder. The for-
mation of this compound, which contains two azine rings, may be
represented by the following equation : —

n TIT AT /^6W2 .NJJCgJJ^-4tl-

CJLN

CJT-,

-N —

— N:

— X-

CJL

Fluorindines are also produced by heating orthodiamines aiul
by heating a mixture of diamidophenazine and orthophenyleue-
diamine [45].

The fluorindines are blue or violet compounds. In sulphuric
acid or alcoholic solutiou they exhibit a magnificent brick-red
fluorescence which is very characteristic.

QUIXOLINK ANU ACKIDINE DYESTUFFS.

207

CHAPTER X.

QUINOLIXE AND ACRIDINE DYESTUFFS.

QuiNOLixE and Acridine aud their liomologues belong to the
chroraogens. The chromogen character is but slight, and is only
inconsiderably developed by introduction of amido-groups. The
simple amido bases form yellow salts^ which are, however, not
dyestuflfs. These are formed, however, by introduction of an
araidated benzene residue. *•

This is the case with flavaniline and chrysaniline, which are
derivatives of phenylquinoline and phenylacridiue respectively —

-CJI^XH,

xn..

Flavaniline.

CeH.NHa
Chrysaniline.

Another class of dyestuffs is known in which quinoline does not
appear to be the real chromogen. The fact that these bodies
cannot be obtained from pure quinoline, but only in presence of
its homologues, gives reason for the assumption that they are
analogous to the phenylmethane dyestufPs, and that a methane
carbon atom links together several quinoline rings.

These dyestuffs include the cyanines, quinoline red, and pro-
bably quinoline yellow (?).

208 CHEMISTRY OF ORGANIC DYESTUFFS.

Cyanine [2, 3, 4, 5].

On heating a mixture of quinoline and lepidine (methylquino-
line) [4j M'itli an alkyl iodide in presence of an alkali, a blue dye-
stuff is formed, which contains one molecule of each of the bases
and the alcohol radical used twice. It is also formed by treating
a mixture of the alkyl iodide compounds of quinoline and lepidine
with alkali [4], One molecule of hydriodic acid is split off and
the iodide of cyanine formed.

The cyanines are strongly basic compounds ; the iodine can
only be removed from the iodides by silver oxide.

The monoacid salts are crystalline and of a beautiful blue
colour. With weak acids, often even with carbonic acid, they are
converted into the colourless di-acid salts [2, 5].

The cyanines dye blue shades, which are, however, too sensitive
to light and acids to be of practical value.

Dimethijlcyanine [4]. — The iodide C^iHigNal is formed from the
methyl iodides of quinoline and lepidine. It forms lustrous
green needles, M.P. 291°. Its blue solution is decolorised by
carbonic acid. The ethyl iodides of the above bases form the corre-
sponding cyanine iodide C03H23N2I.

An isomeric cyanine is formed if quiualdine is used in place of
lepidine [4].

Isoamylcyanine, discovered by Greville Williams [5] and ex-
amined later by Hofmann [2] , is best known. According to Hof-
mann it is formed from pure lepidine and possesses the composition
C30H39N2I. In all these iodides the iodine may be replaced by
other acid radicals.

It is possible that the cyanines are constituted similarly to the
phenylmethane dyestuffs, the methyl group of the lepidine fur-
nishing the methane carbon atom. The cyanines belong to the
earliest artificial dyestuffs, the first representative having been
discovered by Greville Williams in 1856.

Qainolme Bed

is obtained by action of benzo-trichloride on coal-tar quinoline in
presence of zinc chloride [1,6]. According to Hofmann's re-
searches there are two different dyestuffs of this class, one of

QUIXOLIXE AND ACRIDIXE DYESTUFFS. 209

which is derived from qiiinoline and quinaldine and the other from
quinaldine and isoquiuoline.

The isoquiuoline derivative is easier to prepare and a far better
yield is obtained.

The quinoline red from isoqninoline has the composition
CacHigNs. It is a base and forms a hydrochloride of the formula
C.jeHigNo^^^^- ^* crystallises in thin quadratic leaflets or in
larger prisms. It is sparingly soluble in cold water_, easily in hot,
and is separated again by an excess of hydrochloric acid.

The platinum double salt has the formula (Co6Hi9N2Cl)2 PtCl^.

On heating quinoline red with ammonium sulphide, benzyl mer-
captan is split oflP, and. a compound, of the composition CigHi^Ng
is formed.

On dry distillation it yields a base of the composition C17H15N.

Quinoline red. may be regarded as analogous in constitution to
the triphenylmethane dyestuffs, the methane carbon atom of the
benzotrichloride entering into two quinoline residues.

It gives a magnificent eosine-red. shade on silk, and exhibits a
fluorescence which surpasses that of every other dyestuff. The
shades are, however, extremely sensitive to light.

Quinoline Yelloio (Quixophthalox) [1, 6]. -
CisHnNO^.

Is formed by action of phthalic anhydride on quinaldine or on
coal-tar quinoline containing quinaldine in presence of zinc
chloride. Quinoline yellow crystallises from alcohol in fine yellow
needles, M.P. 235°. It is insoluble in water and ether, pretty
easily soluble in hot alcohol and glacial acetic acid, and easily ia
strong sulphuric acid. It has no basic properties and dyes wool
and silk yellow. Its sulphonic acid, obtained by treating with
fuming sulphuric acid, dyes wool and silk pure yellow like picric
acid. Basic dycstuffs may be obtained by heating Avith ammonia
under pressure. Probably these are formed by substitution of
oxygen by nitrogenous groups.

The homologues of quinaldine yield similar dycstuffs with
phthalic anhydride [7].

A similar dyestuff, pyrophthalon, of the composition Ci^ITgNOj,
is obtained from coal-tar picoliue and phthalic anhydride [7] .

210 CHEMISTRY OF ORGANIC DIESTUFFS.

In all these reactions, plitlialic anlndride may be replaced by
the anhydrides of the chlorinated jihthalic acids.

Owing to its high price quinoline yellow has only found a limited
application. It gives very fast shades, and would be valuable in
dyeing i£ the cost of production were less. It is applied solely as
sulphonic acid and is dyed like the acid dyestuffs. The shades
produced are pure yellow, free from any tinge of red.

Fara-amido])henyl-y-leindine {Flavaniline) [8, 9, 10].

This dyestufF is prepared by heating acetanilide with zinc
chiloride to 250°-270°. The melt is extracted with hydrochloric
acid, and the flavaniline precipitated by addition of salt and acetate
of soda. The yield is very small.

Flavaniline is a strong base ; it forms long colourless needles,
sparingly soluble in water, easily in alcohol and benzene, M.P. 97°.
It may be distilled without decomposition. The monoacid salts
of flavaniline dye wool and silk pretty pure yellow shades.

Hydrochloride, Ci6Hi4N2,HCl, forms yellowish-red prisms with
a bluish-red reflex. It is easily soluble in water.

Dihydrochloride, Ci6Hj4N2j(HCl)2, is a white salt obtained by
adding concentrated hydrochloric acid to the aqueous solution of
the former. It is decomposed by water or on heating.
Ci6Hi4N22HCl,PtCl4 forms a yellow crystalline precipitate.
Ethyl flavaniline is obtained by action of ethyl iodide on an
alcoholic solution of the base.

Iodide, CieHi3N2(C2H5)HI, forms long ruby-red needles.
Flavaniline contains an amido-group, and forms a diazo-com-
pouud which is converted into flavenol, CjcHigNO, on boiling with
water. This compound exhibits weak basic and acid properties.
It forms colourless leaflets, which may be sublimed with partial
decomposition, M.P. 128°. It forms colourless salts with acids.
On distilling with zinc powder it yields a new base — flavoline,
CieHisNg. This latter compound forms colourless lustrous crystals,
M.P. 65°. It yields monoacid salts.

The behaviour of flavoline on oxidation shows it to belong to
the quinoline series. By oxidation Avith permanganate it yields
first lepidine carbonic acid,

QUINOLIXE AND ACRini.VE DVESTUFFS.

COOH

on fiirtlicr oxidation picoline tricarbonic acid^

C5HN (COO 11)3,

^CHa
and finally pyridine tetracarbonic acid, C5NH(COOH)4.
These facts show that flavoline is a methylphenylquinoline

cir.

211

Flavenol is therefore an hydroxyl- !^r^d flavaniline an aniiJo-
derivative of this compound, Tlie constitution of flavaniline is
expressed by the formula :

cri.

-C,H4^'IL

An interesting synthesis of flavaniline was effected by O.
Fischer. It consists in the condensation of equal molecules of
ortho- and para-amidoacetophenone, according to the equation :

CII,

XII,

+ II..0

/XII,

212 CHEMISTRY OF ORGANIC DYESTUFFS.

Probably the formation of flavaniline from acetanilide and
zinc chloride is due to a molecnlar change of the acetanilide
to the isomeric amidoacetophenones, Avhich then form flavaniline.

Berlerine.
C20H17NO4.

Berberine is an alkaloid occurring in many plants, and be-
longs to the quinoline dyestuffs. So far as our present know-
ledge reaches, it is the only member of this series occurring in
nature, and is also the only natural dyestuff with basic properties
capable of being fixed on fibres like basic aniline dyes.

Berberine has been found in many plants. The largest quan-
tities are found in Calumba roots {Coccu/uft pabnatus) [19], and in
the roots of Berberis vulgaris, Linn. [20], The latter is the
only one of importance in dyeing.

Pure berberine forms yellow needles, sparingly soluble in
alcohol and in water. It loses water of crystallisation at 100^
and melts at 120°. It is a monoacid base forming soluble crystal-
line salts with acids. The nitrate C20H17N 0^,11 NO3 is especially
noteworthy for the case with which it .forms large crystals ; it is
insoluble in excess of nitric acid. Berberine is capable of forming
lakes with metallic oxides. The dry hydrochloride is turned red.
by chlorine. On melting with potash it yields quinoline and. two
acids, one of which, C.sHgO^, appears to be homologous with
proto-catechuic acid [16]. On oxidation with nitric acid,
berberine gives pyridine tricarbonic acid [17, 18].

Reducing agents convert berberine to colourless hvdro-berberine,
C20H21NO4 [16].

In dyeing, berberine is used in form of a decoction of the
berberis roots. On animal fibres it is dyed from a neutral bath,
and on cotton it is fixed, with tannic acid. It is almost exclusively
used for dyeing leather.

Chrysanilines.

C19H15N3 and C20H17N3.

The chrysanilines are formed in small quantities as bye-products
in the manufacture of magenta, both by the arsenic acid and the

QUIXOLIXE AXD ACRIDINE DYESTUFFS. 213

nitrobenzene processes. They are separated from the first magenta
niothcr-liquors by partial precipitation with soda, and are finally
rystallised from pretty strong nitric acid. The chrysaniline
vamined by Hofmann [11] has without doubt the formula
C20H17N3 ; but recent researches by Fischer and Koerner [12]
render it probable that crude chrysaniline contains two homo-
logous -bases, CigHj^Ng and C00H17N3. At least the analytical
results obtained by Hofmann cannot be brought in unison with
the formula Ciylii.^Ng set up by the latter chemists.

The chrysaniline C20H17N3 [11], when precipitated from its
salts by alkali, forms a liglit yellow powder similar to precipitated
lead chromate. It is almost insoluble in water, dissolves easily in
alcohol, benzene, and ether. The two latter solutions exhibit a
beautiful yellow-green fluorescence. The base may be distilled
with partial decomposition. Chrysanili)ie forms two series of
salts with acids, both of which are yellow to orange in colour.
With the exception of the picrate and the hydriodide, the salts
are soluble in water, but sparingly soluble in an excess of acid.
On dilution, the diaeid salts are split up into monoacid sale and
water.

Nitrate, C2oHi7N3,HN03, forms orange-yellow needles, sparingly
soluble in cold water, easily in hot. From the solution, nitric
acid precipitates the diaeid nitrate, Co,Ji 17X3,211X03, in orange-
yellow clusters of needles. Chrysaniline is capable of with-
standing the action of pretty strong nitric acid.

If impure chrysaniline is dissolved in strong nitric acid, the
nitrate crystallises out on standing, and this property is utilised in
the purification of the dyestuff.

The hjdrochlorides, CoJIi7N3,HCl and Co^,Hi7X3,2HCl, are
more easily soluble than the corresponding nitrates.

Picrate, C2oHi;N32(C6H.(NOo)30H) + HoO, forms red needles
insoluble in water and sparingly soluble iu alcohol.

TrimethylchrysanUine, Coolly (Cli3)3X'3. The dihydriodidc,
^'soHulCHs) 3X3(111)2, is formed by heating chrysaniUne, methyl
iodide, and methyl alcohol to 100° for five hours. It forms orange-
red needles, soluble in hot water. On adding ammonia to the
hot solution, the mono-hydriodide separates in yellow needles.
The base may be obtained from these iodides by action of silver
oxide. It forms easily soluble salts with most acids.

C2uHu(CH3)3N3(HCl)3,PtCl4 forms yellow felted needles.

214

CHEMISTRY OF ORGANIC BYESTUFFS.

The corresponding ethyl derivatives may be obtained in an
analogous manner by the action of ethyl iodide. Amyl derivatives
have also been prepared [11].

Chrysaniline CioHjgNg [12] "«as obtained by Fischer and
Koerner from commercial chrysaniline. The base crystallises
from benzene in clusters of golden-yellow needles, containing one
molecule of benzene, Avhich is expelled on drying. It melts at
upwards of 200^, and distils with partial decomposition.

Clirysojjhenol CjgHujNoO [12] is formed by heating the above
compound with concentrated hydrochloric acid to 180°.

It forms small orange needles, forming salts with acids, and also
reacting like a weak acid towards alkalies. It dissolves in soda,
forming a light yellow solution from which acids precipitate it as
an orange precipitate.

On heating with acetic anhydride, chrysaniline yields a diacetyl
compound [13], C]j)Hi3Ng(C2H.^O)2, which still possesses basic
properties, forming monoacid salts with acids.

Ci9Hi3N3{C2lI.^O)oHCl forms long yellow needles, easily soluble
in water [13].

The corresponding nitrate is sparingly soluble.

By treating chrysaniline, C19H15K3, with nitrous acid, two
nitrogen atoms are converted into diazo-groups. On boiling the
resulting diazo-compound with alcohol, phenylacridine is formed :

CeHg

It follows therefore that chrysaniline is a diamidophenylacri-
dinc [12].

An interesting synthesis of chrysaniline was effected by Fischer
and Koerner [12].

Orthonitrobenzaldehyde condenses Avith aniline to form ortho-
nitroparadiamido-triphenylmethane, which on reduction yields
orthodiparatriamido-triphenylmethane :

QUINOLINE AND ACRIDIN'E DYESTUFFS.

215

—Nil,,

NH..

This compound yields chrysanilinc on oxidation.

As in the formation of acridine the nitrogen and carbon
atoms take up ortho positions in both benzene-nuclei, chrvsauiline
has the followinjj constitution :

—XII.,

For a considerable period clirysaniline was the only basic
yellow dyestuff, and for this reason was largely used in cotton-
dying. Wool and silk are dyed directly, cotton requires a tannin
mordant. The shade produced is an orange-yellow, noteworthy
for its fastness to liiiht.

216 CHEMISTRY OF ORGANIC DYESTUFFS.

At present clirysaniline, which is used as nitrate or hydro-
chloride, under the name of Phosphine, has hut a Hmitcd applica-
tion in silk and cotton-dyeing.

The reason for this is that there is no good method for pro-
duction of phosphine, and as its preparation from magenta-
residues is somewhat complicated^ its price is relatively high.

Acridine Yellow [22].

This dyestuff is a hydrochloride of diamidodimethylacridine of
the constitution :

^N^^ \NH2.HCl.

ch;

For its preparation formaldehyde is condensed with metatoluy-
lenediamine, and the resulting body treated with acid, ammonia
splits off, and the resulting leuco-base is oxidised. It dyes silk
yellow with green fluorescence.

Acridine Orange.

Acridine orange is according to its formation a tetramethyl-
diamidoacridine :

(CH3)oNCeH3/ I >CeH,N(CH3).3,

and is obtained by heating of tetramethyltetramidodiphenylme-
thane with acids and subequent oxidation of the resulting leuco-
acridine. Acridine orange is a basic dyestuff producing reddish-
orange shades on cotton.

Benzoflamne.

A diamidophenyldimethylacridine isomeric with chrysaniline
been brought into commerce under the above name.

QUINOLINE AND ACRIDIXE DYESTUFFS.

217

According to a patent of C. Odiler, it is obtained in tlie
following manner [21] : —

Metaplicnylenediamine, or metatoluylenediamine, is condensed
with beuzaldeliyde^ forming tetramidotriphenylmetliane or its
homologues. The latter base on heating with acid loses one
molecnle of ammonia, yielding diamido-hydrophenylacridine, the
leuco-base of benzoflavine, which is formed on oxidation :

NIL,

Nil,

Tetramidotriplieiiylmetliane.
NTI

NIL

CII
I

Diamidohydroplienylaciidine.
N

Nil.

Nil,

U
I

Coll,

Benzoflavine.

Benzoflavine comes into commerce as a yellow powder. It is
easily soluble in hot water, and the solution solidifies to a jelly on
cooling. From the solution concentrated hydrochloric acid pre-

218 CHEMISTRY OF ORGANIC DYESTUFFS.

cipitates the sparingly soluble orange hydrochloride. The free
base precipitated by an alkali forms a light yellow powder^ which
dissolves in ether with a beautiful greeu liuorescence, similar to
that of chrysaniline.

The dyestuff dissolves in concentrated sulphuric acid with a
light yellow colour, which becomes orange on dilution.

The shades produced on wool, silk, and on cotton mordanted
with tannic acid resemble those with auramine. They may be
distinguished by their behaviour towards concentrated hydro-
chloric acid, benzoflavine becoming orange, while auramine is
destroyed. Tlie stability of benzoflavine towards acids is a decided
advantage, but it does not appear to be so fast to light as
auramine.

INDIGO DYESTUFFS. 219

CHAPTER XL

INDIGO DYESTUFFS.

Tin: colouring-matters of the indigo group^ of whicL the most
important is indigo blue, are derivatives of indol. This compound
is closely related to pyrrol, both as regards constitution and pro-
))erties. The relationship existing between indol and pyrrol is
analogous to that of benzene to naphthalene, or of pyridine to
quinoline, and is best shown by the following formulae : —

CH— CH<. ^Cli^

II .CH CJI,. CH

CH— NH / ^ NH^

Pyrrol. Indol.

The nitrogen and carbon atoms of the side ring occupy ortho
positions in the benzene ring, and form with the third carbon atom
a closed chain containing five members [1, 2] ,

Indol, like pyrrol, possesses slight basic properties, and also
colours a strip of fir, moistened with acid, red. It forms colour-
less leaflets, M.P. 52°, which have a peculiar, unpleasant smell. It
boils at 245° with partial decomposition. With nitrous acid it
yields a nitroso-derivative. Of the salts, only the picrate is stable.
AVith acetic anhydride it forms acetyliudol.

Indol was first obtained by reduction of indigo blue. It is also
produced in the pancreatic digestion of albuminoids [2], and by
melting the latter Avith potash.

It may be obtained synthetically by heating orthonitrocinnamic
acid with potash and iron filings, and by passing diethylortho-
toluidine through a red-hot tube.

Indol is also formed by melting carbostyril Avitli caustic potash
[7], by distillation of nitropropeuylbeuzoic acid with lime [8], by
heating orthoamidostyrol with sodium ethylate [9], by passing

22) CHEMISTRY OF ORGANIC DYESTUFFS.

tetrahydroqiiinoline through a red-hot tube [10], aud by treating
ortlionitrophenyhicetaldehyde with zinc powder and ammonia [11] .

A general synthetic method for production of alkyl-indols is
that of Emil Fischer.

Ketones react with phenylhydrazine to produce hydrazones :

C6H,NH.Nn, + CO<'^[]^ = CJl5XHN = C<[j{|^ + ILO.

The hydrazones, on heating Avith zinc chloride, split off one
molecule of ammonia, with production of a substituted indol :

CJI,-NII-NC<^gj = CJlX^J{)CCH3 + NH3.

Substituted hydrazines yield the corresponding substituted in-
dois; for example, from diphcuylhydrazine and acetone diplieuyl-
indol is formed :

C'6H4.^ CH.

DERIVATIVES OF INDOL.

Lidoa'i/l.

^C(OH).^

This hydroxy-indol occurs in the urine of herbivorous animals
as indoxylsulphuric acid. Indol is converted into indoxyl-
suiphnric acid in the animal organism. From this compound
indoxyl is formed by warming with concentrated hydrochloric
acid. It may also be obtained by heating indoxylic acid, accord-
ing to the equation :

CsH7N03=C8H;XO + C03 [13].

Indoxyl is an oil not volatile in a current of steam. On oxi-
dation it gives indigo blue.

Indoxylsulphuric acid may be obtained by heating indoxyl
with potassium pyrosulphate [1-]. It exists only in the form of
its salts. These are colourless and yield indigo blue on heating
or on oxidation.

INDIGO DYESTUFFS. 2.21

Indoa-ylic Acid,

The ethyl ether of this acid is formed by reduction of orthonitro-
phcnylpropiolic acid ethyl ether with ammonium sulphide [13].

The free acid is obtained by saponification of the ether with an
alkali. It forms a crystalline precipitate, sparingly soluble in
water. It splits up into indoxyl and carbonic acid on heating.
Oxidising agents convert it to indigo blue, while on heating with
concentrated sulphuric acid indigo sulphonic acid is formed.

0.muM\\i, 24],

CeH O.

^NII^

This compound is an inner anhydride of orthoamidophcnyl acetic
acid, and is isomeric with indoxyl. It is formed by reduction of
isatin with sodium amalgam [14], and of acetylorthoamidophenyl-
glycollic acid with hydriodic acid [15]. It forms colourless
needles, !M.P. 120°, and exhibits simultaneously basic and acid
properties. It reacts with nitrous acid, producing isatinoxime
[-24].

JUioxindol,

^'CHOH.
CeH, ^CO,

^ HN

is the inner anhydride of orthoamidophenylgly collie acid. It is
the first product of the reduction of isatin with zinc powder [14].
It forms colourless prisms, M.P. 180°. On heating strongly,
aniline is formed. It oxidises in aqueous solution, forming first
isatyde, and then isatin. Reducing agents convert it to oxindol.
Dioxindole is a dibasic acid, but also possesses slight basic pro-
perties. Its acetyl derivative is decomposed by baryta water,
acetylamidophenylglycollic acid being formed. It yields a nitroso-
derivative with nitrous acid.

222 CHEMISTRY OF ORCAXIC DYESTUFFS.

Isafin.

This corapoimcl is the inner anhydride of orthoamidophenylgly-
oxylic acid :

^CO— COOII

Isatin is formed by oxidation of indigo with nitric acid or
chromic acid [IG]. It may also be obtained by oxidation of
amido-oxindol, and of carbostyril [18] ^ and by boiling ortho-
nitrophenylpropiolic acid with caustic-potash sohition. Further
methods of formation are given under tlie synthesis of indigo-
blue.

Isatin forms orange ])risms, M. P. 200°. It is sparingly solul)le
in water, easily in alcohol and ether. It possesses the properties
of a weak monobasic acid, but also reacts like the aldehydes and
ketones ; for example, it combines with bisulphites of the alkalies,
and with phenylbydrazine and its sulphonic acids [65].

By oxidation w^ith dilute nitric acid it yields nitrosalicylic acid,
and on melting with caustic potash, aniline is formed. By oxi-
dation with chromic acid in acetic-acid solution anthranilcarbonic
acid (Kolbe's Isatoic Acid) [21] is produced:

/CO

^X— COOH

Phosphorus pentachloride converts isatin to isatin chloride :

C6H4X. /CCl.

Isatin forms a blue condensation-product (indophenine) with
thiophene. On reduction with ammonium sulphide, isatide
C16H12X2O4 [16] is formed. With zinc powder in acetic-acid
solution, isatin yields hydroisatin ; by more energetic reducing-
aerents oxv- and dioxv-indol are formed. Chlorine and bromine
react with isatin, forming chlorine and bromine derivatives
respectively. Acetic anhydride produces an acetyl isatin [15],

INDIGO DYESTUFFS. 223

probably a derivative of pseudo-isatin. Isatin chloride yields
indigo blue on reduction, indigo-purpurin being sometimes formed
as a bye-product [22] . Isatin forms ethers with the alcohol radi-
cals. The methyl ether of isatin yields a condensation-product,
methyl isatide, C17H12N0O4. Isatin combines with hydroxyla-
mine, forming an oxime, CgHgNoOo [25], which is identical with
the nitroso-oxindol discovered by Bayer and Knop [14, 21]
(pseudo-isatin, see constitution of the Indigo group).

Isatin is capable of yielding condensation-products with hydro-
carbons [58]. In the formation of these bodies one oxygen atom
of the isatin is replaced by two monovalent hydrocarbon rests.
From their behaviour these bodies appear to be derivatives of
pseudo-isatin ; the toluene derivative has accordingly the formula :

(€7117)3

Similar condensation-products may be obtained with tertiary
bases and phenols. They yield dyestuffs on oxidation, which i)ro-
bably belong to the triphenyl methane series [58].

The compound formed from isatin and thiophene has the
formula :

C12H7NOS [58].

Inclolin, see 62, 63.

Isatic Acid.
p „ /CO— COOH.

(Orthoamidophenylglyoxylic acid, orthoamidobenzoylformic acid.)
The salts of this acid are formed on heating isatin with a strong
solution of caustic alkali. The free acid may be obtained bv de-
composition of the lead salt with sulphuretted hydrogen [26], or
synthetically by reduction of orthonitrophenylglyoxylic acid with
ferrous sulphate and caustic soda. The acid is unstable, its aqueous
solution decomposes on boiling, isatin and water being formed.
Acetylisatic acid is formed by treating acetylisatin with a cold
solution of a caustic alkali [15].

224 CHEMISTRY OF ORGANIC DYESTUFFS.

Isatogenic Ether [13, 27].

^co— c.coo.aH,

N— O

This body is isomeric with the ether of orthonitrophenylpropiolic
acid, and is formed on treating the latter with concentrated sul-
phuric acid. It forms yellow needles, M.P. 115°.

Diisatofjen [27],
CO— C— C— COv

N — O O— N^

is formed on treating dinitrodiphenyldiacetylene with concen-
trated sulphuric acid. It forms red needles, soluble only in
chloroform, nitrobenzene, and strong sulphuric acid. It is easily
converted by reducing agents to indigo blue.

Indoxanthic Ether [28].
CO— C(OH)CO,C2H5.

PR/ ^
NH

This compound is obtained by oxidation of indoxylic ether with
ferric chloride. It forms straw-yellow needles, M.P. 107°. Alka-
lies convert it to anthranilic acid. It forms a nitrosamine with
nitrous acid ; on reduction indoxylic ether is reproduced.

Inii go-Blue.
C6H4— CO— C=C— CO— CgH^.

NH NH

Indigo blue is the most important, in fact the only important
derivative of iudol from a technical point of view.

INDIGO DYESTUFFS. 225

Indigo occurs as a glucoside, indican, in various plants {Indi-
gofera tinctoria, Indigofera anil^ Polygonum tinctorium, and Isatis
tinctoria). According to Schunck [29], indican from Isatis tine-
toria has the composition CgeHgiNOi;, and decomposes according
to the equation :

2C26H3iNOir + 4H2O = C16H10N2O2 + CeHioOe.

Indigo-blue. Indiglucine.

It is, however, uncertain if the same indican occurs in all plants.

In the industrial preparation of indigo, an aqueous extract of the
plants is submitted to fermentation. The indigo blue produced is
probably reduced by the sugar, soluble indigo white being formed.
On subsequent oxidation in the air, indigo blue separates mixed
with various impurities. The crude product obtained in this
manner is the valued dyestuff known as indigo. The amount of
pure colouring-matter (indigotin) contained in indigo varies,
being generally between 20 and 90 per cent. Besides this, it con-
tains various substances : indigo red, indigo brown, indigo yellow,
and indiglutin, of most of which but little is known.

Indigotin occurs sometimes in urine.

Indigotin is best obtained from indigo by conversion of the
latter into the soluble reduced compound, and subsequent oxida-
tion by air [30] (indigo vat) . Another method consists in ex-
tracting the indigo with aniline or chloroform and allowing the
indigotin to crystallise from the solvent. According to the
method of preparation, indigotin forms lustrous coppery needles
or a dark blue powder. On heating it does not melt, but sublimes
with partial decomposition in form of coppery needles. Indigo
vapour has a purple-red colour.

Indigotin is insoluble in most of the usual solvents. It dis-
solves in aniline, chloroform, nitrobenzene, phenol, paraffin,
petroleum, naphthalene, and in certain fatty oils. The solutions
have not all the same colour ; for example, the aniline and chloro-
form solutions have a deep indigo-blue colour, while the solution
in paraffin has the purple-red colour of indigo vapour, a behaviour
somewhat similar to that of iodine.

The composition of indigotin corresponds to the formula
CsHgNO, but from determination of its vapour-density, the
molecule contains twice this and is therefore C16H10N2O2.

Indigotin dissolves unchanged in concentrated sulphuric acid

226 CHEMISTRY OF ORGANIC DYESTtlFFS.

with a green colour. On heating, sulphonic acids are formed, the
colour of the solution changing to blue.

By destructive distillation, indigotin yields aniline ; on melting
with caustic potash, aniline, anthranilic acid, and salicylic acid are
formed [16].

Oxidising agents convert indigotin to isatin [16]. Chlorine
produces chlorine derivatives of isatin first, and then chlorinated
phenols and chloranil [16] . Bromine acts in a similar manner.

Indigotin dissolves in hot concentrated caustic potash solution
with an orange-yellow colour, indigo white and isatic acid being
probably formed.

On reduction in alkaline solution indigo blue takes up two
atoms of hydrogen, forming indigo white, which possesses phe-
noloid properties and dissolves in the alkaline liquid.

In the air, indigo white solution oxidises immediately, insoluble
indigo blue separating. This property is extensively employed in
dyeing with indigo, and also serves for the isolation of pure indigo
from the commercial product.

The reducing-agents more commonly employed are ferrous salts,
arsenious acid, stannous oxide, hyposulphurous acid, zinc powder,
and grape-sugar.

Dihenzoylindigo [32],
CacH8N202(G,H,0)2,

is formed on heating indigotin with benzoyl chloride.

Halogen derivatives [33] of indigotin have been prepared from
the corresponding derivatives of isatin and of orthonitrobenz-
aldehyde [37].

Dinitro- and diamido-indigotin have been prepared from
dinitro-isatin [33] . (Compare the '^ Synthesis of Indigo Blue,'^
p. 231.),

Indigo Wliite,
C16H12N2O2,

is formed by reduction of indigotin, and contains two atoms of
hydrogen more than the latter. In distinction from indigotin,
which possesses neither basic nor acid properties, it exhibits the

INDIGO DYESTUFPS. 227

character of a weak acid like the phenols. It dissolves in alkalies,
and may be precipitated from the solutions by an acid. Carbonic
acid separates it as a silky greyish-white mass. Indigo white can
only be dried and preserved in an atmosphere of carbonic acid or
hydrogen. It oxidises rapidly to indigotin on exposure to the
air. From the properties of indigo white^ it is apparent that the
carbonyl oxygen atoms of the indigotin are converted into
hydroxyl groups.

From the derivatives of indigo blue (sul phonic acids, &c.),
substitution-derivatives of indigo white are obtained on reduction.

Indigo Blue Sulphonic Acids.

Monosulphonic Acid [34],
Ci«H,N,0,S03H,

{Sulphopurpuric Acid.)

This acid is obtained by heating indigo with concentrated sul-
phuric acid. It forms purple-red flocks which dissolve in pure
water with a blue colour, but are insoluble in dilute sulphuric
acid. The salts are sparingly soluble in water, insoluble in saline
solutions.

Disulphonic Acid [34],
CieHsNAlSOaH)^,

is formed by further action of sulphuric acid on indigotin. It
forms an amorphous powder, soluble in water. The salts are also
easily soluble, and may be separated from aqueous solutions by
addition of salt. The sodium salt comes into commerce as a paste,
and is known as Indigo Extract, Indigo carmine, &c. It is
applied like the acid dyestuffs, and has a somewhat extensive
application in wool-dyeing. Indigo-disulphonic acid may also be
obtained synthetically, the method will be found under Synthesis
of Indigotin.

228 CHEMISTRY OF ORGANIC DYESTUFFS.

Application^ of Indigo in Dyeing.

The tinctorial properties of indigo are due to the presence of
the chromophorous group :

•which forms a closed chain with the benzene ring. As it contains
no salt-forming groups it is not a real dyestuff, and owing to its
insolubility has no affinity for the fibre. This may be produced by
introduction of sulpho-groups, and the indigo then assumes the
character of an acid dyestuff. The principal application of indigo
depends, however, on its conversion into soluble indigo. The
process based on this property is termed vat-dyeing, and has been
in use since the earliest periods. Most of the reducing-agents
acting in alkaline solution have been applied, but in practice the
following are important : — Ferrous sulphate, stannous chloride,
grape-sugar, arsenious acid, zinc powder, and sodium hydro-
sulphite.

The reducing-agent employed is generally added along with
lime or soda to a finely divided indigo suspended in water. The
ferrous sulphate and stannous chloride are hereby converted to
the corresjjonding hydrates. The indigo blue is slowly converted
to indigo white, which dissolves in the alkaline liquid. The indigo-
vat is used for dyeing both wool and cotton.

Wool apj)ears to have a certain attraction for indigo white and
is capable of withdrawing it from solution, while cotton is only
impregnated with the liquid. In all cases the conversion of
indigo white to indigo blue on the fibre is effected by atmospheric
oxidation. Only in recent years has indigo been applicable for
direct printing. Previously calico was dyed in an indigo- vat, and
then the necessary effects produced by printing on discharges.
Of late years, however, the following methods have been employed
on direct printing.

Cotton fabrics impregnated with grape-sugar solutions are
printed with a mixture of finely divided indigo and strong caustic
soda suitably thickened. On steaming the indigo white produced

INDIGO DYESTUFFS. 229

thoroughly penetrates the fibre, and on oxidation fast indigo
effects are obtained.

The difficulties in this direction have also been to a certain
extent vanquished by the introduction of artificial indigo. A
thickened mixture of orthonitrophenylpropiolic acid and grape-
sugar, or better an alkaline xanthate with an alkali is printed,
and the indigo blue developed by steaming and drying.

However, orthonitrophenylpropiolic acid does not appear to have
made serious competition with natural indigo in this direction,
and interesting as the synthesis is from a scientific standpoint, it
has not yet been applied practically to any great extent.

Indigo carmine is almost exclusively used in wool-dyeing, and is
applied in an alum bath at the boil.

The shades obtained are finer than those from the vat, but are
not so fast. They are principally used in production of mixed
shades.

Indigodicarhonic Acid [36],
CieHsNAlCOOH)^.

This acid is formed by treating nitroterephthalaldehydic acid,

COOH 1

CeH,

-COH 4,

:no, 2

with acetone and soda solution, and by action of alkali and grape-
sugar on the carbonic acid of orthonitrophenylpropiolic acid. It
forms a blue precipitate, insoluble in chloroform. The solution
with alkalies is green, and is precipitated by acids.

Indoine [13],
CsoHsoN^Og.

Indoine is formed by reduction of orthonitrophenylpropiolic
acid with ferrous sulphate in sulphuric acid solution. It closely
resembles indigo, but may be distinguished by the following
reactions : — It dissolves in cold concentrated sulphuric acid with a
blue colour (indigo gives a green solution), and is only converted
into a sulphonic acid with difficulty. It is also easily soluble in
aniline and in aqueous sulphurous acid, forming blue solutions.

230 CHEMISTRY OF ORGANIC DYESTUFFS.

Indigopurpurin.

This compound is isomeric with indigotin, and is formed as a
bye-product in the preparation of the latter from isatin chloride
[22, 38].

It is similar to indigotin, but is more readily sublimed, forming
fine red needles. It dissolves in alcohol with a red colour. On
dissolving in concentrated sulphuric acid and diluting with water,
it gives a red solution.

Indiruhin [13, 60].
CgH^— CO-C-::C— C(OH)=N.

X / \^ /

NH CcH^

Indirubin is the indogenide of isatin, and is isomeric with
indigotin. It may be obtained by mixing aqueous solutions of
indoxyl and isatin in presence of a little caustic soda.

Indirubin forms a reddish-brown powder. It dissolves in
alcohol with a violet colour, and in concentrated sulphuric acid
with a greyish-black colour. The latter solution becomes violet
on heating, a sulphonic acid being formed. With reducing-agents

gives a vat, and on further reduction indileucin, CigHioNgO, is
produced.

From the present state of our knowledge, it is not certain if
mdigopurpurin and indirubin are identical or different.

Indigo Red [61].

This compound, which occurs in crude indigo, is also an isomer
of indigotin. The exact relationship existing between this body
and the two previous ones is not certain. According to Baeyer, it
differs from indigopurpurin.

Schunck obtained a compound from indican which he named
Indirubin, and which he regards as identical with indigo-
purpurin [61].

INDIGO DYESTUFFS. 231

Indigo red forms a vat and a sulphonic acid, both capable of
dyeing. The shades produced in the vat are noteworthy for their
extreme fastness to light.

SYNTHESIS OF INDIGO BLUE.

In the years 1865 and 18GG Baeyer and Knop [14] converted
indigotin through dioxindol and oxindol into indol ; and
three years later Baeyer and Emmerling [5] prepared indol
synthetically by melting a mixture of nitrocinnamic acid, caustic
potash, and iron filings. The nitrocinnamic acid employed was a
mixture of the ortho and para compounds, and only later was it
discovered that the ortho acid is alone capable of yielding indol.
In 1870 the same chemists observed the formation of indigo
blue by treating isatin with a mixture of phosphorus trichloride
and acetyl chloride.

In the same year Emmerling and Engler [39] obtained small
quantities of indigo by heating nitroacetophenone with zinc
powder and soda-lime, but subsequently were unsuccessful in
producing the necessary conditions for the formation of the
dyestuffs.

The first certain method for producing artificial indigo is due to
Nencki, who obtained it by oxidation of indol with ozone [40] .
The same chemist had already obtained indol by the pancreatic
fermentation of albumen [2, 40]. In 1877 Baeyer and Caro
obtained indol by passing the vapour of certain aromatic amines,
especially of diethylorthotoluidinc, through a red-hot tube.

In 1878 the constitution of oxindol was discovered by Baeyer
[17] and by Suida [15]. It was found to be the inner anhydride
of orthoamidophenylacetic acid, and was obtained synthetically
from the latter.

In the same year [17] Baeyer prepared isatin from oxindol.
The nitroso-compound of oxindol yields the amido-compound on
reduction, and this is converted into isatin by oxidation or by
nitrous acid.

As isatin had already been converted into indigo, the forma-
tion of the former from orthoamidophenylacetic acid eff'ects a
complete synthesis of indigo. At the same time Baeyer [17]
improved the process whereby isatin was converted into indigo.

232 CHEMISTRY OF ORGANIC DYESTUFFS.

Isatin is first submitted to the action of phosphorus tri- or penta-
chloridcj and the resulting isatin cliloride yields indigotin on
reduction. In this case indigopurpurin is formed as a bye-
product.

Claisen and Shadwell discovered a new synthetical method for
production of isatin in 1879. By action of silver cyanide on
orthonitrobenzoyl chloride, orthonitrobenzoyl cyanide is produced,
and this is converted into orthonitroplienylglyoxylic acid by
saponification and subsequent treatment with an alkali. On
reduction of this acid in alkaline solution, a salt of isatic acid
(orthoamidophenylglyoxylic acid) is produced, from which isatin
may be separated by an acid.

These researches effect another complete synthesis of indigotin.

In 1880 Baeyer prepared indigo synthetically from cinnamic
acid by various processes [19, 41] : —

I. Orthonitrocinnamic acid,

CH=CH— COOH [1]

NO2 [2]

unites with bromine to form orthonitrodibromhydrocinnamic acid,

CHBr-CHBr-COOH [1]
CeH/

NO2 [2]

On treating this compound with alkalies, two molecules of
HBr split off and an unsaturated acid — orthonitrophenylpropiolic
acid,

C=C-COOH [1]

. NO2 [2]

is formed. This acid yields isatin on boiling with an alkali, and
indigo on reduction in an alkaline solution (alkaline grape-sugar
solution, or an alkaline xanthate).

II. By treating orthonitrocinnamic acid with chlorine in
alkaline solution, orthonitrophenylchlorlactic acid is formed
according to the equation :— -

INDIGO DYESTUFFS. 233

CHOH-CHCl
CH = CH-COOH / I

CfiH/ +HC10 = CeH, COOH.

NO2

This acid gives orthonitrophenyloxyacrylic acid on treating with
an alkali,

CeH,<

CH-CHCOOH

NO2

On heating in phenol, or glacial acetic-acid solution_, this com-
pound yields indigo.

III. Orthonitrophenylpropiolic acid yields orthonitrophenyl-
acetylene on boiling with water [42] :

C=CH
C6H,<

NO,

On oxidation of the copper compound of the latter with potas-
sium ferricyanide, dinitrodiphenyldiacetylene is produced :

c=c— c=c
N02 N03

On treatment with fuming sulphuric acid this body undergoes
a molecular change, an isomer, diisatogen, being formed. The
latter gives indigo on reduction [42] .

IV. In 1882 orthonitrobenzaldehyde was used as a starting-
point for the artificial production of indigotin [2].

On dissolving orthonitrobenzaldehyde in acetone and adding
an excess of dilute caustic-soda solution, indigo blue separates on
standing. The acetone may be replaced by acetaldehyde or
pyinivic acid. This reaction was studied in detail by Bacyer [44].
The interaction of acetone and orthonitrobenzaldehyde results in
the formation of an intermediate product of the composition
C10H11NO4 (probably the methyl ketone of orthonitrophenyl-lactic

234 CHEMISTRY OF ORGANIC DYESTUFFS.

acid). This compound decomposes under the influence of alkalies
according to the equation :

2CioHnN04 + 2H2O = C16H10N2O2 + 2C2H4O2 + 4H2O,

indigotin and acetic acid being formed.

With acetaldehyde, orthonitrobenzaldehyde forms the aldehyde
of orthonitrophenyl-lactic acid :

/CHOH-CH2COH,

p T T / i >

which splits up with alkalies^ forming indigotin and formic acid
[45] . The intermediate product in the case of pyruvic acid is
orthonitrocinnamyl-formic acid [44] :

/CH=CH— CO— COOH.
^^^^\N02

This body is best obtained by action of gaseous hydrochloric
acid on a mixture of the reacting compounds. Orthonitrocinnamyl-
formic acid is S2)lit up by alkalies into indigotin and oxalic acid.

A patent of Meister, Lucius, & Briining [46] depends on a
similar reaction. Claisen^s benzylidene-acetone (cinnamylraethyl-
ketone CcHg — CH = CHCO — CH3) [47], obtained by condensation
of benzaldehyde and acetone, is nitrated. A mixture of ortho and
paranitro derivatives is formed, and. the former yields indigotin
by action of alkalies.

Ortho-nitrometa-tolualdehyde [48] gives a homologue of indigo-
blue, and chlorine derivatives may be obtained from chlor-ortho-
nitroaldeliydes [37] . Another method has its starting-point in
ortho-amidoacetophenone. This compound is converted into its
acetyl derivative and treated with bromine in the cold. The re-
sulting bromine derivative, when dissolved in concentrated sul-
phuric acid, loses hydrobromic acid, a crystalline compound being
formed, which, under the influence of air in presence of alkalies,
yields indigotin.

Indigotin may also be obtained from ortho-amidophenylacety-
lene by an analogous process.

Gevekoht [50] obtained indigotin by action of ammonium sul-
phide on ortho-nitroacetophenone, in which the methyl group is
brominated.

INDIGO DYESTUFFS. 235

From the researches of Baeyer [51] and Bloem it is shown that
on brominating acetylortho-amidoacetophenone, the bromine atom
enters in the methyl group. If the benzene ehain is substituted
brominated indigos are formed ; but if only the benzene chain con-
tains bromine, indigo cannot be produced. Tn these reactions
indoxyl appears to be formed as an intermediate product in the
reaction.

P. Meyer [52] prepared substituted indigo blues from the
corresponding substituted isatins. This process depends on the
fact that the final products of the action of dichloracetic acid on
amines in which the para position is occupied are substituted
isatins. The first product of the action of dichloracetic acid on
paratoluidine is a paratolylimide derivative of paramethylisatin,
C^eHigNaO, which decomposes on boiling with acids into para-
toluidine and methylisatin, C9H7NO2.

Perhaps the simplest methods for the synthetic production of
indigo are those which have their starting-point in certain aniline
derivatives of acetic acid. Flimm discovered that bromacetanilide,
CgHgNH — CO — CHgBr, gives a trace of indigo on heating with
caustic potash (B. B. 1890, p. 57), Heumann^s process gives a
somewhat better result, but still the yield (about 15 per cent.) is not
sufficiently great for technical application. In this method phenyl-
glycocine, formed by action of monochloracetic acid on aniline, is
heated with caustic potash with exclusion of air to about 260°.
The orange-yellow melt obtained is dissolved in water, and on ex-
posure to air indigo separates. The course of the reaction is not
exactly understood, but in all probability the first stage consists in
the formation of pseudoindoxyl :

CfiH. . NH . CH5CO OH

/CO.
= H20-^C6H4( )CHo.

In alkaline solution pseudoindoxyl oxidises immediately, pro-
ducing indigo :

r. „ /C 0\ /C O. /C O^

236 CHEMISTRY OF ORGANIC DYESTUFFS.

A somewhat better result is obtained by using phenylglycocine-
orthocarbonic acid, which is prepared by action of monochloracetic
acid on anthranilic acid. This compound is fused with caustic
potash, the reaction taking place at a considerably lower tempera-
ture than when phenylglycocine is employed.

If phenylglycocine is mixed with sand and introduced into a
large quantity of sulphuric acid containing a considerable amount
of sulphuric anhydride, taking care to avoid an increase in tem-
perature, a reaction immediately takes place, sulphurous acid being
evolved, while the solution takes a blue colour. This is due to
the formation of indigo-disulphonic acid, which may easily be
isolated by dilution and addition of salt. The yield by this pro-
cess is satisfactory, amounting to about 60 per cent, of the phenyl-
glycocine used.

CONSTITUTION OF THE INDIGO GROUP.

From his synthesis of indol from orthonitrocinnamic acid
Baeyer ascribed to it the constitutional formula :

s\ A

\NH/

H.CeC >CH,

which is now generally accepted.

Kekule had already (1869) [53] published an opinion that
isatin is an inner anhydride of orthoamidophenylglyoxylic acid,
and accordingly suggested the structural formula :

.CO.
CeHX >C0.
NH^

Claisen and Shadwell proved that isatic acid is orthoamido-
phenylglyoxylic acid, and that isatin is its inner anhydride by a
direct synthesis [26]. However, various properties of isatin
noted by Baeyer speak for the presence of an hydroxyl group
according to the formula :

.CO.
CsHX >coh.

INDIGO DYESTUFFS.

237

Oxindol is, from its synthetic production, an inner anhydride
of orthoamidophenylacetic acid, and has the formula :

The formation of oxindol and dioxindol by reduction of isatiu
is, however, more in favour of the following constitution for these
compounds : —

Dioxindol.

,CH(OH)COH

c«h/

CH2— C(OH)

Oxindol.

The constitution of indoxyl may be deduced by its formation
from indoxylic acid :

^C(OH)=C— CO3H

C6H4'

The hydroxyl group must be in combination with the carbon
atom in the adjacent position to the benzene ring. The constitu-
tion of indoxyl is accordingly represented by the formula

C6H4'

.C(OH)— CH

NH'

From certain reactions it appears probable that isatin, indoxylic
acid, and indoxyl are capable of existing in two isomeric forms.
One of these exists only in the form of derivatives (for example,
ethers) . Baey^r terms these " labile or pseudo forms,'' and gives
the following formuhc to them : —

CgHi^

CO-COH

Isatin.

C6H4C(OH)=CH

\NH^

Indoxyl,

/CO.— CO

^NH/

Pseudoisatin.

C6H4— CO— CH2

\nh/

Pseudoindoxyl.

238 CHEMISTRY OF ORGANIC DYESTUFFS.

C6H4— C(OH) ^C— COOH CgH^— CO— CH— COOH

ludoxylic acid. Pseudoindoxylic acid.

These pseudo-modifications are stable when certain of their
hydrogen atoms are replaced. In the case of pseudoisatin a
monovalent group suffices ; while in pseudoindoxyl both hydrogen
atoms of the carbon atom in the side-ring must be replaced. In
this manner the following compounds may be obtained : —

CeH^-CO— CO CfiH^— CO— C=CHC6H5

NC2H5 ^NH^

Ethylpseudoisatin. Benzylidenepseudoindoxyl.

The divalent rest of pseudoindoxyl,

C6H4--CO— C=

is especially interesting, as researches on this subject show that it
must be contained in indigotin. Baeyer designates this rest as
the iudogene group, and those derivatives in which the indogene
group replaces an atom of oxygen are termed indogenides. The
above benzylidenepseudoindoxyl must therefore be regarded as
the indogenide of benzaldehyde, as it is formed by heating indo-
xylic acid with benzaldehyde, carbonic acid and water splitting off.
Indigotin may be regarded as a combination of two indogene
groups, as expressed by the constitutional formula :

CgH^- CO— C=:C— CO— CeH^

Indigotin.

This constitution is also that of an indogenide of pseudoisatin :

/CO— CO

CeHX ^ .

and indigotin is therefore formed by replacement of an oxygen

INDIGO DYESTUFFS. 239

atom of pseudoisatin by the indogene group. Similarly, iudi-
rubin is the indogenide of isatin :

CgH^— CO— C=C— C(OH)=N

Indirubin is formed by action of isatin on iudoxyl, in which
reaction it must be accepted that the latter undergoes a molecular
change into pseudoindoxyl.

Baeyer arrives at these conclusions from the following facts : —
By the action of nitrous acid on indoxyl a nitrosamine of the
latter is formed :

^C(OH)=:CH
C6H4X ^..^^--^

NfNO)

On reduction it is converted through indoxyl to indigotin.
By action of nitrous acid on ethylindoxylic acid [56] an isomeric
compound, possessing the properties of an isonitroso compound, is
formed. It yields isatin on reduction and subsequent oxidation.

It is probable that in the formation of this body from ethyl-
indoxylic acid :

.C (O— C2H5) =C— COOH,
CeHX _

a molecular change takes place, as two monovalent groups are
split off from two different carbon atoms, and the isonitroso group
is always divalent and connected with one carbon atom.

The formation of isatin from this body shows it to be pseud-
isatoxime or isonitrosopseudoindoxyl :

CO— C=NOH.

CeHX ^

This constitution receives further support from the behaviour
on ethylation, whereby a mono-ethyl ether is produced. This ether
also yields isatin, and therefore cannot contain the ethyl group
in direct combination with a carbon atom, nor yet in the iraide
group. It is stable to hydrochloric acid, which would not be the
case were the ethyl group connected with hydroxyl.

240 CHEMISTRY OF ORGANIC DYESTUFFS.

The constitution of the compound is therefore expressed by the
formula :

CO— C=NO(C2H6)

It is pseudoisatinethyl-a-oxime. On further ethylation the
diethyl ether is formed :

CO— C^NOCgHs

NC2H5

'\^

On reduction and subsequent oxidation, ethylpseudoisatin is
formed :

/CO— CO
CeH/ ^_-
NCoH,

It differs from the isomeric ethylisatin by being difficult to
saponify. Alkalies convert it to ethylisatic acid :

^CO— COOH
^NHC^Hs

With hydroxylamine ethylpseudoisatin gives the /3-oxime

.C(NOH)— CO

C6H4N

NC2H5

It combines with indoxyl to form the indogenide
C6H4— CO— C=C— Co— NC2H5

^^^NH ^^^^CeH^

The diethyl ether of pseudoisatin-a-oxime yields diethyl
indigo blue if treated with mild reducing- agents, precisely in the
same manner that pseudoisatoxime gives indigo blue under similar
conditions.

As in this reaction the ethylated isonitroso group is split off,
while the ethyl group attached to the imide-nitrogen atom remains
intact, it follows that if the above constitution of ethyl pseudo-

INDIGO DYESTUFFS. 241

isatin ethyl a-oxime is correct, diethyl-indigotin must possess
the constitution expressed by the formula :

C6H4-CO— C=C_CO— CeH^ ;

NC2H5 NC2H5

and consequently iudigotin the analogous one :
CeH^— CO— C=C— CO— CfiH,.

NH NH

Baeyer summarises the conclusions leading to this formula as
follows : —

1. Iudigotin contains an imi do-group.

2. Its formation from diphenyl-diacetylene shows that the
carbon atoms are placed in the following manner : —

CgHs — C — C — C — C — CgHs.

3. Iudigotin is formed only from those compounds in which the
carbon atom adjacent to the benzene ring is connected with an
atom of oxygen.

4. The formation and properties of iudigotin show a close
relationship to indirubin and to the indogenide of ethylpseudo-
isatin. The latter is formed by the coupling of the a-carbon
atom of pseudoindoxyl with the y9-carbon atom of pseudoisatin.

242 CHEMISTRY OF ORGANIC DYESTUFFS.

CHAPTER XII.

EUXANTHIC ACID AND GALLOFLAVINE.

These yellow clyestufFs, though of totally different origin, show
some relationship in chemical properties, and possibly owe their
tinctorial value to the same chromophor. In euxanthic acid this
is a carbonyl group, which forms a ring with one oxygen atom and
two benzene nuclei.

Euxanthic acid contains as chromogen the rest of diphenylene-
ketone-oxide :

q/C6R4\qq^

^CeH/
somewhat similar in constitution to anthraquinone,

co(^«^*)co.

It has not been determined with certainty that galloflavine
contains the same group.

Huocantliic Acid.
CioHisOii.

The magnesium salt is the essential constituent of the dyestuff
known in commerce as Purree or Indian Yellow. This product is
obtained from the urine of cows, fed on mango-leaves. The gold-
yellow urine is heated, and the yellow deposit formed into a ball.
This is purified by removing the outer portions and thoroughly
washing the remainder.

The recent researches of v. Kostanecki [8] demonstrate that the
origin is from urine, as they proved that the urine of animals whose
food contained euxanthone separated euxanthic acid. It is probable

EUXANTHIC ACID AND GALLOFLAVINE. 243

that the euxanthone contained in certain plants combines with
glucuronic acid in the animal organism, euxanthic acid thus being
formed. To prepare euxanthic acid, purree is exhausted with water^
treated with dilute hydrochloric acid, and the residue extracted
with ammonium carbonate. The resulting ammonium salt is de-
composed with hydrochloric acid, and the euxanthic acid crystallised
from alcohol (2).

It forms lustrous straw-yellow needles, sparingly soluble in cold
water, more easily in hot water, and readily in alcohol, but in-
soluble in ether.

On heating to 130° one molecule of water splits off, an anhydride,
CijjHieOi,, [6], being formed. This was formerly regarded as
anhydrous euxanthic acid, the crystallised acid having the formula
C]<,Hi60i„ + H20. Euxanthic acid is monobasic; its salts with the
alkalies are easily soluble, those with magnesium and lead sparingly
soluble. The alkali salts are precipitated, by an excess of alkali.
On heating with water or dilute sulphuric acid to 140°, euxanthic
acid splits up into euxanthone [1], CisHtjO^, and glucuronic acid,
C,H„0, [6].

Euxanthone is also formed by heating euxanthic acid to 160-180°,
or by warming with concentrated sulphuric acid [38] .

Chlorine and bromine act on euxanthic acid, producing di-sub-
stitution products [2] . Nitric acid produces nitro-euxanthic acid
in the cold ; on warming, trinitro-euxauthone, and finally styphuic
acid is formed [1] .

Euxanthone.
CisHsO,.
This compound forms pale yellow needles which sublime without
decomposition. It is insoluble in water, sparingly soluble in ether,
easily in boiling alcohol. It is formed as described, above from
euxanthic acid, and is also a constituent of purree, the lower
(jualities containing most. It is soluble in aqueous solutions
of the alkalies, but possesses no further acid, properties. Its
alcoholic solutionis precipitated by lead acetate. On heating with
zinc powder, benzene, phenol, and methylenediphenylene-oxide,
CHo— (CeH4)20 [9], are formed. The last-named compound
yields diphenyleneketone- oxide on oxidation,

244

CHEMISTRY OF ORGANIC DYESTUFP8.

Diacetyleuxantlione is formed ou boiling euxanthone with acetic
anbydiidCj M.P. 185°. Dichloreuxantlione and dibromeiixanthone
maybe produced by decomposition of the corresponding derivatives
of euxanthic acid [2].

Trinitroeuxantlione forms vellow needles, and is a monobasic acid

[2].

The constitution of euxanthone is explained by the following re-
searches of Baeyer and Graebe [21] . On melting with potash it
yields euxantlioiiic acid (tetraoxybenzopheuone)_,

OH OH

CO —

which on further heating splits up into resorcin and hydroquinonc,
Euxanthone is the inner anhydride of euxanthonic acid,

— 0 —
— CO-

and is therefore 2.6 dioxydiphenyleneketone-oxide. This is con-
firmed by its synthesis, on heating hydroquinone carbonic acid with
/3-resorcylic acid in presence of acetic anhydride.

Euxanthic acid is apparently an ether of euxanthone (or euxan-
thonic acid) with glucuronic acid.

C,,UsO, + CeHioOz = CioHisOn.

Eusauthone. Glucuronic Euxanthic
acid. acid.

Euxanthone, although yellow, is not a dyestuff, while euxanthic
acid is capable of dyeing on metallic mordants.

Its principal application is as an artists' pigment under tlie name
of Indian Yellow.

EUXAXTHIC ACID AND OALLOFLAVINE. 2 i5

Synthetical Oxyketone Dyestuffs [22].

A method for the productioa of hydroxyl derivatives of benzo-
phenone and its homologaes has been patented by the Badischc
Anilin- und Sodafabrik.

The process consists in heating fatty or aromatic acids with
a phenol or oxycarbonic acid containing at least two hydroxyl
groups in the ortho position to each other with a dehydrating agent.
The reaction may be best explained by the following example.

Trioccyhenzophenone.

One part of pyrogallol and one part of benzoic acid are heated
to 145°, and tliree parts of zinc chloride gradually stirred into the
mixture, and the above temperature maintained for three hours.
The melt is extracted with boiling water, and on cooling the dye-
stuff is deposited in yellow needles, M.P. 137-138°. It dyes
golden-yellow shades on cotton mordanted with alumina ; the
presence of lime-salts renders the tone more orange. Another
process for production of trioxybenzophenone, due to the same
firm, consists in heating pyrogallol with benzotrichloride in
aqueous, alcoholic, or acetic acid solution. It is known in com-
merce as Alizarin Yellow A.

Gallaceto^henone.

This compound is a trioxyacetophenone ] (OHjgCeHoCOCHg^,
obtained by heating pyrogallol with acetic acid and zinc chloride
to 150°. It may be used for printing with chromium acetate, and
gives brown shades [23]. It is named Alizarin Yellow G.

Ellagic Acid.

This compound is related to the above dyestufts and to gallo-
flavine, although its constitution has not been determined with cer-
tainty. Ellagic acid may be obtained by action of various oxidising
agents on gallic and tannic acids, and by heating gallic ether with
soda solution. It also occurs naturally in bezoar stones. Ellagic acid
gives greenish-yellow shades when printing with chromium acetate.

24G CHEMISTRY OF ORGANIC DYESTUFFS.

Galloflavine.

This dyestuff is formed by oxidation of a gallic acid solution,
containing about two molecules of an alkali^ by atmospheric oxygen
[12]. It is best prepared by dissolving gallic acid in alcoholic
potash solution, and passing a current of air through the solution.
A potassium salt of the dyestuff, which is sparingly soluble in
alcohol, separates [11].

Galloflavine forms greenish-yellow leaflets, sparingly soluble in
ether and alcohol, more easily in acetic acid, and best in aniline. It
is soluble in alkalies, and is reprecipitated on the addition of acids.

The composition of galloflavine is jirobably represented by the
formula CigHyOg.

It forms dibasic salts ; those with the alkalies are easily soluble
in water.

If heated with acetic anhydride, it yields a colourless acetyl
compound, C^^Yi^O^{Q.,^^0)/,^l.V. 230° [11].

Galloflavine is used along with metallic mordants. On alumina
it produces a greenish-yellow shade, on tin oxide a pure yellow,
and on chromium oxide an olive-green. It has been used to
a slight extent in wool-dyeing; on chromed wool it gives results
similar to fustic.

CANARINE. 247

CHAPTER XIII.
CANARINE. [13,14,15.]

On treating potassium sulphocyanide with potassium clilorate, ia
presence of hydrocliloric acid, canarine is formed (ProkorofF and
Miller) [IS].'

This compound is probably identical with that discovered by
Liebig [16], and named pseudo- or persulpho-cyanogen, C3N3HS3,
although the identity of the two is denied by Miller.

Canarine forms a yellow powder, insoluble in neutral solvents,
soluble in alkalies and in borax solution.

The application of canarine depends on its property of dyeing
cotton yellow from an alkaline solution. The shades vary from
light yellow to orange-yellow^ according to the concentration of
the solution. They are very fast both to soap and light. In com-
parison with other artificial dyestuffs, canarine only possesses weak
tinctorial properties.

Canarine dyed on cotton is capable of acting as a mordant for
basic dyestufPs. In this respect it resembles Cachou de Laval and
the benzidine series of direct colours.

248 CHEMISTRY OF ORGANIC DYESTUFFS.

CHAPTER XIV.

MUREXIDE. [17, 18, 19, 20.]

MuREXiDE is the acid ammonium salt of purpuric acid, which docs
not exist in the free state. It is of historical interest, as besides
picric acid it is the oldest artificial dyestuff used technically. Its
application dates from the year 1853.

Murexide is obtained by action of ammonia on the mixture
of alloxan and alloxautin, obtained by evaporating a solution of
uric acid in strong nitric acid.

It is formed further by heating alloxantin in ammonia gas, and
boiling uramil with mercuric oxide.

It forms four-sided prisms, with a green lustre, appearing red
by transmitted light.

The composition of murexide is expressed by the formula
CgH^NgOgN H4. By double decomposition with potassium nitrate, .
the potassium salt (CgH^NgOgK) is obtained. The salts with
calcium, barium, tin, and mercury are sparingly soluble red or
violet precipitates.

Murexide dissolves in water with a fine purple-red colour, which
is changed to blue-violet on addition of excess of alkali. Mineral
acids set free purpuric acid, which immediately decomj)oses into
uramil and alloxan, the solution being decolorised.

Murexide may be dyed on tin, lead, or mercury mordants, the
last producing the best results. It is at present out of use.

DYESTUFFS OF UNKNOWN CONSTITUTION. 249

CHAPTER XV.

DYESTUFFS OF UNKNOWN CONSTITUTION.

The following chapter comprises those dyestuffs which cannot be
placed under the foregoing chemical classifications. It has already
been mentioned that many of the dyestuffs treated of under the
previous groups are of unknown constitution ; but, being products
of chemical synthesis, certain relationships to the various classes
are easily deduced.

The number of colouring-matters included in the present chapter
is unfortunately very large ; most of them are natural products
obtained from plant and animal sources. As these natural dyestuffs
are very numerous, only those are described which are of interest
from a technical or scientific point of view.

Although the artificial dyestuffs have to a great extent replaced
the natural ones, certain of the latter still retain great importance
in dyeing, being in fact indispensable, as no synthetical products
have been able to do their work.

The great importance of a large number of the natural dyestuffs
is based on the property which they possess of forming firmly-
adherent lakes with metallic oxides. They are, like alizarin,
adjective dyestuffs.

Some of them, for example Haematoxylin, Haematein, Brasilia,
and Brasilein, are possibly quinones ; others appear to be related
to Euxanthone.

Some of these compounds are glucosides, which may be split up
by action of dilute acids, forming a sugar, and a compound which
is the real colouring-matter.

Somenatural dyestuffs (Curcumin,Bixin,Carthamin) are capable,
like the tetrazo dyestuffs, of dyeing on unmordanted cotton.

250 CHEMISTRY OF ORGANIC DYESTUFFS.

Hoematoxylin [1, 2, 3, 13].

Haematoxylin is contained in logwood or campeachy, the wood
of Hcematoxyhn campechianum. Although scarcely a dyestuff,
hseraatoxylin is the only important constituent of logwood, as on
oxidation it yields haematein [2] , a compound of strong tinctorial
properties.

Hematoxylin is prepared by extracting freshly rasped logwood
with aqueous ether, evaporating, and mixing the residue with
water [3] . The crystals which separate are recrystallised from
water, preferably with addition of ammonium bisulphite to prevent
oxidation.

Hasmatoxylin crystallises with 3 H2O in colourless tetragonal
prisms [4], or witli 1 HjO in rhombic crystals. It dissolves
sparingly in cold water, and is dissolved with facility by hot water,
alcohol, and ether. It has a sweet taste. It melts in its water of
crystallisation somewhat over 100°. Its solution turns a ray of
polarised light towards the right [3].

It dissolves in alkalies with a purple colour ; the colour rapidly
changes, with formation of haematei'n, to blue-violet, afterwards
becoming brown. Chromic acid, ferric chloride, and vanadic acid
form higher oxidation products, which give black lakes with
metallic oxides. On melting with potash, or on dry distillation,
it yields pyrogallol and resorcin [99] .

Formic acid has also been observed amongst the products
formed in the potash melt [99] .

Bromine acts on haematoxylin in acetic acid solution, forming
a dibromo derivative. Acetic anhydride yields a pentacetyl
derivative, Ci6H906(C2H30)5, M.P. 165-166°, which on treating
with bromine combines with four atoms, and by cautious bromi-
nation a monobromo derivative may be produced [6, 13, 99].
Nitrous and nitric acid convert haematoxylin to hsematein ; the final
product of oxidation with nitric acid is oxalic acid.

Hcemafe'in [2, 3, 7].

Hsematem is produced by careful oxidation of haematoxylin
with nitric acid [5], or by action of atmospheric oxygen on an

DYESTUFFS OF UNKNOWN CONSTITUTION. 251

alkaline solution of this body [2, 3]. It is best obtained by
exposing an ethereal hsematoxylin solution mixed with a few drops
of nitric acid to the air.

It forms dark green masses with a metallic lustre or lustrous
silvery leaflets, which form a red powder on rubbing [5, 100].
It is sparingly soluble in hot water, alcohol, and ether, forming
yellowisii-brown solutions. Its alkaline solutions are bluish
violet. The ammonia compound, CigHi206,2NH3, is sparingly
soluble and evolves ammonia on heating [3j. On treating with
aqueous sulphurous acid, hjEmatein is dissolved without reduction,
and forms easily soluble colourless addition compounds, which are
decomposed on boiling. More stable compounds are obtained
from haeniatei'n and bisulphites.

Hffimate'in forms peculiar addition products with hydrochloric,
hydrobromic, and sulphuric acids, which are decomposed by water
at a high temperature [8] .

In dyeing and printing, hsematoxylin and hsematein are used in
form of logwood extract or decoction.

Haematoxylin produces a greyish-violet shade on alumina mor-
dants, probably due to formation of hamatein by oxidation.
Copper salts produce a dark blue, iron salts and chromic acid a
deep black. In practice, several of these mordants may be applied
simultaneously; for example, logwood may be printed on an
alumina mordant and afterwards passed through a bath of
potassium bichromate or copper sulphate. The lakes with iron
and chromium are derived from higher oxidation products which
have as yet been little examined.

Logwood is largely used in cotton, wool, and silk dyeing. For
wool, it serves especially for producing black on iron and
chromium mordants. The wool is generally mordanted in a bath
of bichromate and sulphuric acid and dyed in a logwood bath.
Cotton is dyed black by alternate passages through logwood and
bichromate baths. For production of a deep black without a
violet tone, the addition of fustic or a similar yellow dyestuff is
necessary. A mixture used in dyeing and printing, under the
name of indigo substitute, is composed of logwood extract and
chromium acetate.

252 CHEMISTRY OF ORGANIC DYESTUFFS.

Brazilin [1, 9, 10].

^16111405.

Brazilin occurs in the wood of various species of Ccesalpinia,
especially in Ccesalpinia brasiliensis, and with brazile'in forms the
essential constituent of the dyewoods known as Brazil-wood, Peach-
wood, and Sapan-wood.

Brazilin often separates from the commercial extract of the dye-
wood in form of crystalline crusts [9] , and these are the best material
for a pure preparation of the compound. These crystals contain
brazilin mixed with its calcium compound, and on boiling with
very dilute alcohol, with a little hydrochloric acid and zinc
powder, a solution is obtained from which brazilin crystallises on
cooling.

Brazilin crystallises from water, according to the concentration
of the solution, in clear amber rhombic crystals containing 1 HgO,
or in colourless needles [10] with 1^ HgO. It dissolves pretty
easily in water, alcohol, and ether. Alkalies give a carmine-red
solution, which is decolorised by zinc powder, the colour returning
quickly on exposure to air. On dry distillation it gives large
quantities of resorcin [9] .

By action of nitric acid styphnic acid is formed; potassium
chlorate and hydrochloric acid produce isotrichlorglyceric acid [12] .

On adding lead acetate to an aqueous solution of brazilin. the
lead compound separates in fine colourless needles, CKjHigPbOs
+ H2O, which rapidly turn red. On reduction with hydroiodic acid
and phosphorus, brazilin yields brazinol, CieHj^O^, and finally
CjeHseOs, both amorphous bodies [15]. On distillation with zinc
powder, brazinol gives a hydrocarbon CjeH,^ or CieHie [15].

Tetracetyl brazilin, CigHjoOs (031130)4 [11], and triacetyl brazilin
are formed by treating brazilin with acetic anhydride [14] .

Dibrom- and dichlorbrazilin are formed by cautious bromiuation
and chlorination of brazilin [11, 13].

Brazilin is applied technically in form of extract or decoction
of brazil-wood. It can be fixed only by use of mordants, and is
used both in cotton and wool dyeing. On alumina mordants it
produces shades resembling alizarin, but inferior both in beauty
and fastness. The tin lake has a brighter colour. Wool
mordanted with potassium bichromate is dyed a fine brown
shade.

DXESTUFFS OF UNKNOWN CONSTITUTION. 253

Brazilein [11, 12, 7].

Brazilein bears the same relationship to brazilin that haeraatem
does to haematoxylin. It is formed by oxidation of an alkaline
solution of brazilin in the air and by the action of alcoholic iodine
solntion [11] or of nitrous acid on the same compound.

Brazilein forms grey silvery leaflets, which dissolve sparingly
in water, easily in alkalies with a purple colour. Like hajmatein,
it forms unstable combinations with hydrochloric, hydrobromic,
and sulphuric acids [8]. It resembles brazilin from a tinctorial
point of view, but has greater dyeing power.

Morin [1, 16, 15].

C:oHioOe = Ci,H305 + H,0.

Morin is the colouring-matter of fustic, the wood of Morus
tinctoria ( Jacq.) or Macluria tinctoria (Nettel) . It is best prepared
by boiling the wood with water and decomposing the lime com-
pound with hydrochloric acid [17]. '■ Morin crystallises from
alcohol in long yellow needles. It is insoluble in water and carbon
disulphide, sparingly soluble in ether, and easily in alcohol. It
dissolves in alkalies with a dark yellow colour.

On dry distillation morin yields resorcin and paramorin. On
treatment with sodium amalgam or by melting with caustic
potash it yields phloroglucol, oxalic acid being also formed in the
latter case [18].

Lowe ascribes to morin the formula C15H10O7 + 2 H2O [16].

It acts as a monobasic acid, the salts of the alkali metals are
easily soluble, those with lime, aluminium, lead, and zinc almost
insoluble [18].

Tribromraorin, CjoHyBrgOg, is formed on treating morin with
bromine [18].

Paramorin, Cj^HgO^, formed by dry distillation of morin, forms
yellow woolly crystals easily soluble in water, and which volatilise
unchanged [19].

Isomorin [18] is formed by incomplete reduction of morin
with sodium amalgam. It forms purple-red prisms, and yields
morin on treatment with alkali or on heating. A compound
known as maclurin or morintannic acid, CisHiyOg, is also contained
in fustic, but is not a dyestuff.

254 CHEMISTRY OF ORGANIC DYESTUFFS.

Morin is used largely in wool and cotton dyeing as decoction
or extract of fustic. Its principal application is in shading blacks,
browns, &c. Wool is generally mordanted with potassium bichro-
mate and sulphuric acid. The morin is fixed as a very stable
chromium lake, which has a dull yellow colour.

Youny fustic, the wood of Rhus cotinus, is totally different from
old fustic. Koch isolated the colouring-matter [20 J, termed it
fisetin, and gave it the formula CigHioOg. This has been cor-
rected by recent researches of Schmid [94] . According to this
chemist, the colouring-matter of young fustic occurs as a gluco-
side in combination with tannic acid. This tannin compound splits
up intotheglucoside,fustin,C46H4oOoi,and a tannic acid on warming
with acetic acid. The glucoside splits up with dilute acids into
sugar and fisetin, C23Hio03(OH)6. On boiling with acetic anhydride,
hcxacetyl fisetin, CssHioOgCCaHsO)^, M.P. 200°, is produced.

Hexamethyl fisetin, C23Hio09(CH3)6, is formed by action of
methyl iodide, M.P. 152° and 153°.

The principal use of fisetin is in wool-dyeing, especially for
modifying cochineal scarlets.

Quercitrin [1, 21, 22, 24].
C36H38O20 + 3H2O.

Querciti'in is the colouring-matter of the dyewood known as
quercitron bark, obtained from Quercus tinctoria.

Quercitrin may be obtained as follows : — The bark is boiled
with strong alcohol and the extract precipitated with lead acetate
and acetic acid. The filtrate is freed from lead by sulphuretted
hydrogen, and evaporated. The residue is crystallised from water
[25]. It forms light yellow lustrous needles, which contain one
molecule HjO after drying at 100°, and can be obtained an-
hydrous only by long heating at 130° [21] . It melts at 168° [22] ,
dissolves sparingly in hot water, easily in alcohol. Its solution
gives a green coloration with ferric chloride. Ammoniacal silver
solution is reduced easily ; Fehling's copper solution only after
long boiling.

Quercitrin is a diabasic acid ; the alkali salts are easily soluble,
those with lead and alumina sparingly so. The former is easily
soluble in dilute sulphuric acid.

DYESTUFFS OF UNKNOWN CONSTITUTION. 255

Quercitrin is a glucoside ; on boiling with dilute acids it yields
isodulcite [24], CeHjiOs, and quercin, C^JlieOn. Quercitrin
occurs also in hops^ horse-chestnuts, tea, and many other plants.
Tetrabromquercitrin is obtained by bromination in acetic acid
solution and forms light yellow crystals [25] .

Quercitin [24, 26, 27],

is formed from quercitrin as above, according to the equation :
C36H38O20 + 3HoO = 2C6Hu06 + C24HieO„ [24] .

It also occurs naturally in many plants.

It forms fine lemon-yellow needles, sparingly soluble in water,
but readily in alcohol. It melts above 250°, and sublimes with
partial decomposition. Its solution gives a green coloration with
ferric chloride, which turns red on heating; lead acetate gives an
orange precipitate. Silver nitrate is reduced in the cold, and
Fchling's solution on warming. Nitric acid oxidises it to oxalic
acid. On fusion with caustic potash, quercitin is split up, yielding
querciglucin, CeHgOg (Phloroglucin ?) , and quercitic acid,
Ci^HioO, [28].

At a higher temperature protocatechuic acid is formed. On
reduction of quercitin the final product is phloroglucin [28] .

Amide : by action of ammonia at 150°. Is a brown, amorphous
compound. Dibroraquercitin : light yellow needles. Diacctyl-
dibromquercitin : yellow needles. Tetrabromquercitin : white
needles. M.P. 218°.

Diacetyltetrabromquercitin : white needles, M.P. 226-228°

Quercitin and quercitrin give beautiful yellow shades on cotton
mordanted with alumina. With tin mordants a more orauge shade
is produced. On a large scale these bodies have an extensive appli-
cation, and are used in form of a decoction of the bark or as
flavin. In dyeing with the extract, it is probable that the quer-
citrin splits up, and that the shades obtained are due to the forma-
tion of quercitin lakes.

Flavin consists in some cases of nearly pure quercitrin and in

256 CHEMISTRY OF ORGANIC DYESTUFFS.

others of quercitin. Quercitron and flavin serve principally for
use with cochineal in dyeing scarlet. They are also used in calico-
printing on iron, alnminium, and chromium mordants.

Rutin, the glucoside contained in Chinese yellow berries and in
the leaves of Ruta graveolens, is closely allied to quercitrin. On
boiling with dilute acids it splits up into quercitin and a sugar
[29, 30,31].

Xanthorhamnin, Rhamnetin [32, 33, 34].

Tliesc colouring-matters are contained in Persian berries, the
fruit of Rhamnus bifectoria and oleoides.

Xanthorhamnin (or llhamnegin) is a glucoside of the compo-
sition C^sHoeOag. It may be obtained by extracting the berries
with alcohol. Resinous matters separate and arc filtered off, and
xanthorhamnin crystallises out afterwards. It may be purified by
recrystallisation from alcohol [34]; the crystals obtained contain
two molecules of alcohol, which are expelled at 120°. It is very
easily soluble in water, less easily in alcohol, and insoluble in ether
and chloroform.

It reduces silver nitrate and Fehling's copper solution. Its
solution gives a dark brown coloration with ferric chloride, and
a yellow precipitate with lead acetate and ammonia. On hydro-
lysis with dilute acids it gives rhamnetin and isodulcite ; the same
change may be effected by simply heating to 150°.

On acetylation with acetic anhydride (Schiitzenberger 33), twelve
acetyl groups enter into xanthorhamnin.

Bhamnetin,
C12H10O5 [34],

is formed along with isodulcite, CgHi^Og, by hydrolysis of xantho-
rhamnin. It forms a lemon-yellow powder sparingly soluble in
water, alcohol, ether, and indifferent solvents. It is easily soluble
in phenol, from which it crystallises in yellow needles. It reduces
ammoniacal silver solution and Fehling's copper solution.

Its aqueous solution gives yellow or brownish-yellow precipitates

DYESTUFFS OF UNKNOWN CONSTITUTION. 257

with lead, alumina, barium, and lime-salts. On fusion with
potash, or reduction with sodium amalgam, rhamnetin yields
phloroglucin and protocatcchuic acid.

Dimethylrhamnetin is formed by heating rhamnetin with potas-
sium-methylsulphate, and methyl alcohol to 120°, M.P. 157° [34].

Hcrzig has recently found that the highest products obtained
by methylation of rhamnetin and qucrcitin are identical, and has
further obtained quercitin by removal of a methyl group from
rhamnetin with hydriodic acid. From these results he regards
rhamnetin as a dimcthylquercitin.

Diacetylrhamnetin, M.P. 185° [34].

Dipropionylrhamnetin, M.P. 1G2° [34].

Dibenzoylrhamnet'm, M.P. 210^212°.

These three compounds are obtained by action of the respective
anhydrides on rhamnetin [34] .

Dibromrhamnetin, obtained by broraination of rhamnetin in
acetic acid solution, forms yellow needles soluble in hot benzene,
alcohol, and acetic acid [34] .

Diacetyldibromrhamnetin is formed by bromination of diacetyl-
rhamnetin, M.P. 212° [34].

Xanthorhamnin is not a dyestuif, and it must therefore be
accepted that rhamnetin is formed in the dyeing operations.

Rhamnetin in form of Persian-berry extract is of considerable
importance in calico-printing ; no artificial dyestufF has been found
to replace it with advantage. It is generally fixed as tin or tin-
alumina lake, both of which have a fine yellow colour. The
chromium lake has a browner tone and is also used in printing.
The alumina lake also sometimes used in dyeing has lemon shade ;
its principal application (mixed with chalk) is as an artists^ colour.

Persian berries also contain rhamnin or /Q-rhamnegin, which
yields /3-rhamnetin on hydrolysis [39]. The composition of these
bodies is unknown.

Luteolin [1, 36, 37, 38].

ClsHgOj.

Luteolin is the colouring-matter of weld, the leaves and skin of
Reseda luteola. Luteolin crystallises from alcohol in small yellow

258 CHEMISTRY OF ORGANIC DYESTUFFS.

needles wliicli contain 1^ molecules of water of crystallisation,
which are expelled at 150° [38]. It melts at 320° [36] and may
be sublimed with partial decomposition. It is very sparino;ly
soluble in water and ether; alcohol dissolves it with tolerable
facility.

It dissolves readily in alkalies with a yellow colour, and gives
yellow lakes with lead and alumina salts.

Ferric chloride produces a green coloration, changing to brown
with excess of the reagent.

On fusion with potash, luteolin yields phloroglucin and photo-
catechuic acid [37] .

Luteolin is obtained by extracting weld with dilute alcohol,
evaporating the extract, and recrystallising the compound which
separates.

An aqueous decoction of weld is used in dyeing. On alumina
mordants it produces a beautiful fast yellow. Its principal
application is in silk-dyeing, for which weld is a valuable material.
Silk is previously mordanted with alum.

JBiwin [48, 49, 50, 51],

^28 1134^5 •

Bixin is the principal colouring-matter contained in annatto.
This dyeware consists chiefly of the pulp of the fruit of Bixa
orellana which has been allowed to ferment.

Bixin is , prepared by boiling annatto with alcohol and sodium
carbonate. On adding soda solution to the extract, the sodium
compound of bixin separates; this is purified by recrystallising from
dilute alcohol, and the bixin liberated by hydrochloric acid [51].

Bixin forms dark red metallic leaflets, M.P. 176°. It is almost
insoluble in water, sparingly soluble in cold alcohol, benzene,
glacial acetic acid, and ether, readily soluble in hot alcohol and
in chloroform. Bixin is a dibasic acid. It reduces Fehling's
solution in the cold. It forms a blue solution with concentrated
sulphuric acid, which gives a dirty green precipitate on addition of
water. Sodium amalgam converts it to a colourless compound,
C28H40O5 [51]. On oxidation with nitric acid, bixin yields oxalic
acid. On distillation with zinc powder, it yields metaxylene,
meta-ethyl toluene, and a hydrocarbon Ci^Hj^, ? [51].

DYESTUFFS OF UNKNOWN CONSTITUTION. 259

Bixin gives two sodium salts: NaCgsHsaO-, + HjO, forming
coppery-red crystals, and NaaCosHsaOj, a red powder [51].

Annatto contains a second colouring-matter known as Orellin,
the composition of which is unknown. It dyes a yellow shade on
alumina mordants, and is probably an oxidation product of bixin.

Bixin dyes both animal and vegetable fibres without a mordant.
It is used both in silk and. cotton dyeing in form of annatto. It
is either fixed, directly on cotton, or in form of its tin lake, the
result being a fine orange-yellow shade. Annatto has a large
application in colouring butter and cheese.

Chrysin [52],

C15H10O4.

Chrysin occurs in the buds of the poplar [Poptdus balsamifera
and monUifera) . It forms light yellow needles, M.P. 275°, insoluble
in water, sparingly soluble in benzene, ligroin, and cold alcohol,
easily in glacial acetic acid, aniline, and hot alcohol. It dissolves
in alkalies with a yellow colour. Its alcoholic solution is coloured
dirty violet by ferric chloride, and gives a yellow precipitate with
lead acetate. Chrysin is decomposed on boiling with concentrated
potash solution, forming acetophenone, acetic acid, benzoic acid,
and phloroglucin. On heating with methyl iodide it yields
a monomethylethcr (tectochrysin) , C15H.JO3OCH3, which also
occurs in poplar-buds. It forms thick sulphur-yellow crystals,
M.P. 164°. It is insoluble in alkalies, sparingly soluble in
alcohol, and easily in benzene.

Nitrochrysin, CigHgNOgOj^, is formed by action of nitric acid on
chrysin.

Dibromchrysin, Ci5H8Br204.

Diiodochrysin, CisHglgO^.

Curcumin [53, 54, 55, 56].

This slightly acid colouring-matter is contained in turmeric,
the underground stem of Curcuma longa and C. viridi/lora.

260 CHEMISTRY OF ORGANIC DYESTUFFS.

Curcumin is prepared by steaming turmeric, or extracting with
carbon bisulphide to remove oily matters, and extracting the
residue with ether. The crude product is purified by recrystal-
lisation from ether or benzene. It forms orange-yellow prisms,
M.P. 178° [56]. It is very sparingly soluble in hot water, more
easily in benzene, and readily in alcohol, ether, and fatty oils. It
dissolves in alkalies with a brown colour, and also gives a brown
coloration with boric acid, changing to blue on addition of dilute
alkali [53]. (Reaction for boric acid.) It gives insoluble brown
lakes with lead calcium and barium salts. It dissolves in concen-
trated sulphuric acid with a cherry-red colour.

Nitric acid oxidises curcumin to oxalic acid ; chromic acid
produces terephthalic acid [54] .

Curcumin is extensively used in dyeing, although not fast to
light. Its principal application is in modifying red shades on
cotton, for example saftranine. Curcumin dyes cotton without
mordant. The powdered root is generally used suspended in
water. The cotton is boiled in a mixture, and the curcumin
becomes fixed as it dissolves. An alcoholic extract is sometimes
used, and is mixed with water to an emulsion. Turmeric is also
used for colouring butter, wax, and fatty oils.

Carotin [57, 58, 59],

Carotin is the colouring-matter contained in the carrot {Daucus
carota). It forms rhombic crystals, M.P. 168°, reddish brown in
transmitted light, and gold green by reflected light. It is easily
soluble in carbon disulphide, sparingly in alcohol and ether.
It gives a violet solution with strong sulphuric acid, and is coloured
blue by sulphurous acid. Arnaud [95] regards carotin as a hydro-
carbon, but this assumption is extremely improbable from the
properties of the compound.

Archil and Litmus.

Various kinds of lichens, for example Lecanora tinctoria and
Roccella tinctoria, possess the property of giving violet or blue dye-
stufts when submitted to the joint action of ammonia and air.

DYESTUFFS OP UNKNOWN CONSTITUTION. 261

These lichens contain a number of peculiar acids (lecanoric acid,
erythric acid, roccellic acid, &c.), which are split up by alkalies,
the final products being orcin, C6H3CH3(OH)2, and erythritc,
C4H10O4.

Orcin is the only compound important for the production of
lichen colours ; with air and ammonia it yields orcein, C7H7NO3 ?,
which is the principal dyestuff contained in archil [60, 61, 62, 63].

Orcein gives sparingly soluble lakes with calcium and the
heavy metals, but does not appear to be a real adjective dyestuff.

Commercial archil is prepared by moistening the weeds with
ammonia and exposing the mixture to the air. Formerly putrid
urine was used in place of the ammonia. The product obtained
may be worked up into extract, " Archil liquor ; " or dried and
powdered, or is sold in the crude form as " Archil paste." These
products all contain orcein in form of its ammonia salt.

The dyevvare known as Cudbear is similar to powdered archil.
Besides orcein, archil is said to contain two other colouring-
matters of unknown composition, azoerythrin and erythroleic
acid [60].

Archil is principally employed in wool and silk dyeing, less in
calico-printing. It may be dyed on wool from acid, neutral, or
alkaline baths. An addition of alum, stannous chloride, oxalic
acid, or tartaric acid is made to the dyebath.

The calcium lake is used in printing, and is dissolved in acetic
acid and fixed by steaming {" French purple '') . The shades
obtained with archil are purple, and may be modified with indigo
or cochineal.

Archil has been displaced to a certain extent by azo dyestuffs,
but still has considerable importance in wool-dyeing. This is due
to the various conditions under which archil may be employed,
and it can therefore be used to modify the shades of nearly ail
other dyestuff's.

Litmus.

If the lichens used for the manufacture of archil are submitted
to a longer treatment with ammonia, potash and lime being also
added, the orcin is converted to litmus — a dyestuff which is red
in the free state, and yields blue salts. A similar product may be

262 CHEMISTRY OF ORGANIC DYESTUFFS.

obtained direct from orcin by continued digestion vith a mixture
of ammonia and soda solution [64] .

Litmus comes into commerce in small tablets mixed with cbalk
or gypsum, tlie commercial product containing only a small
quantity of dyestuff.

Litmus is best known as an indicator in volumetric analysis, but
is also used to inconsiderable extent for colouring wine and for
blueing in laundries.

According to Kane (60), litmus contains four colouring-matters —
Erythrolein, Azolitmin, Erytlirolitmin, and Spaniolitmin — the first
two being the most important. It is improbable, however, that
these compounds are chemical individuals.

According to Wartha (61), some kinds of litmus contain indigo.

Carthamin [62],
Ci6HnO,(?).

Safflower, the petals of Carthamus tinctorhis, &c., contains,
besides a yellow dyestuff, a red one, carthamine, which was of
considerable iniportance before the introduction of the artificial
dycstuff's.

To prepare carthamin, safflower is washed with water to remove
the yellow dyestuff, and is then extracted with dilute soda solution,
and filtered. Cotton yarn is immersed in the alkaline solution,
and the liquid acidulated with citric acid. The cotton takes up
the carthamin, which is removed with soda solution, and pre-
cipitated with citric acid. Obtained in this manner carthamin
forms a lustrous green powder, sparingly soluble iu water and ether,
readily in alcohol. It dissolves in alkalies with yellowish-green
colour. On fusion with potash it gives oxalic acid and para-oxy-
benzoic acid. Carthamin dyes animal fibres and unmordanted
cotton from a slightly acid bath. It produces a beautiful pink
colour on silk.

Carthamin enters commerce in a nearly pure state as saf-
flower extract. For dyeing, the extract is dissolved in soda and the
dyebath acidified with citric or other acid. In place of this
extract the soda solution from safflower, which has been extracted
with water, may be directly employed.

Carthamin is also used as rouge in admixture with talc, chalk,
or starch. It is also employed as an artists' colour.

DYESTUFFS OF UNKNOWN CONSTITUTION. 263

The yellow eolouriug-matter of safflower, which according to
Malin has the compositioii CoiHsoOig [63], is of no importance in
dyeing.

Santalin [64, 65, 66].

Sandal-wood or Sanders-wood (from Pterocarpus santalinus)
contains a resinous red dyestuff of slightly acid properties.
Santalin, CigHi^Og, is obtained by precipitating an alcoholic extract
of sandal-wood with lead acetate, and decomposing the lead lake
with dilute sulphuric acid. It crystallises from alcohol in red
prisms, M.P. 104°. It is sparingly soluble in water, dissolves in
alcohol and ether with a blood-red colour, and in alkalies with a
violet colour. It gives violet insoluble lakes with calcium, barium,
and the heavy metals.

Franchimont \Q7'\, who could obtain santalin only in an amor-
phous state, ascribes to it the formula Ci/HieOg. On heating with
hydrochloric acid to 200°, he obtained methyl chloride and an
amorphous body (CgHigOo ?)j which gives a violet-black solution
with alkalies. ^

Santalin is largely used in wool-dyeing and is employed as
rasped sanders-wood, which is directly added to the dyebath. It
produces a good reddish-brown shade on chromed wool, which is,
however, not very fast to light.

An alcoholic extract of sanders-wood is also used for colouring
tinctures, varnishes, and also for staining wood.

AlJcannin [70],
C15H14O4.

Alkanet, the root of Anchusa tinctoria, contains the above red
dyestuff. It is of slightly acid character, and has not been obtained
in a crystalline state. It is insoluble in water, dissolves easily in
alcohol, ether, ligroiu, and fatty oils, forming red solutions. It
dissolves in alkalies with a blue colour, and is reprecipitated by acids
in red flakes. It gives an insoluble lake with baryta. It is pro-
bably a derivative of methylanthracene, C15H12, as it yields this
hydrocarbon on distillation with zinc powder [93] .

The diacetyl compound, C15H 12(031130)20^, is formed by the
action of acetic anhydride and sodium acetate [70].

264 CHEMISTRY OF ORGANIC DYESTUFFS.

Alkannin dissolves in concentrated sulphuric acid with a blue
colour. Nitric acid oxidises it to oxalic acid and succinic acid.

Alkannin (in form of an extract of alkanet root) is used for
colouring oils, pomades, tinctures, &c.

Crocin and Crocetin.

SaiFron, the stigmata of Crocus sativus, contains according to
Quadrat [71] and Weiss [72] a yellow glucoside, polychroite,
C48H68O18 [^3]. According to these chemists it may be split up
into crocin, CieHj^Oe, sugar, and an ethereal oil.

R.Kayser [74] terms polychroit "crocin," and crocin '^crocetir,"
and ascribes to the former the formula C44H70O28, and to the latter
Co^WiiiOc). According to him, crocin splits up into crocetin and
saffron sugar, CeHigOg, while the ethereal oil is a product of the
decomposition of picrocrocin.

L. Meyer [73] and Kochleder obtained crocin from the pods of
Gardenia grandijiora, but it is not certain whether their product is
identical with the above. They obtained a glucoside, CggHgeOsi^
which splits up into sugar and crocetin, C34H3g04. As these bodies
were only obtained in an amorphous state, these formulae appear
to be doubtful.

Lo-Kao (Chinese Gkeen).

The above is a commercial green dyestuff prepared from the bark
of various species of Ehamnus [Rhamnus utilis,Rh. chlorophlorus) .
It consists chiefly of the alumina and lime lakes of the glucoside.

This latter is termed lokai'n by Cloez and Guignet [75], and
lokaonic acid by Kayser \7Q'].

According to Cloez and Guignet a compound has the formula
C28H34O17, and is decomposed by acids, yielding glucose and
lokaetin, CgHgOg [75] . Kayser, on the other hand, gives to lokai'n
(lokaonic acid) the formula C40H48O27, and to lokaetin (lokanic
acid) the formula CggHgeOoj. The sugar produced in the formation
of the latter is not glucose, but an inactive modification which
Kayser terms Lokaose. Loka'in forms a deep bluish-black mass
which takes a metallic lustre on rubbing. It is insoluble in water,
alcohol, ether, chloroform, and benzene, but soluble in alkalies
with a blue colour, which is changed to red by reducing agents.

DYESTUFFS OF UNKNOWN CONSTITUTION. 265

The ammonium salt forms lustrous bronzy crystals. The other
salts are amorphous ; those of the heavy metals are insoluble.

Lokaetin (lokanic acid) forms a violet-black powder only soluble
in alkalies, with a violet colour.

According to Kayser it reacts with sulphuretted hydrogen,
forming a crystalline compound containing sulphur.

Concentrated sulphuric acid produces a brown amorphous eom-
pound_, which is stated to be CjEgO^ by Cloez and Guignet, aud
CaeHaeOie by Kayser.

The formulae for the compounds described above must be re-
garded as doubtful, as the nature of the substances affords little
guarantee for tbeir purity, and the analysis gives little idea of the
true size of the molecules.

Lo-kao is used, especially by the Chinese, for dyeing wool and
silk. It may be fixed on cotton from an alkaline bath, but is also
frequently used in a reduced state as a vat, stannous chloride or
ammonium sulphide being used as reducing agents. The shade
produced is a fine bluish green, very fast to light.

Cochineal.

The important dyeware known as cochineal consists of the dried
female of an insect, the Coccus cacti coccitiellifera, which lives on
certain species of cactus. The colouring principle of cochineal is
glucoside carminic acid, of the formula CiyHi^Oio [77] .

Carminic acid is prepared by precipitating an aqueous decoction
of cochineal with lead acetate, and decomposing the lead lake with
a quantity of sulphuric acid insufficient for the whole. The
solution of carminic acid thus obtained is evaporated to dryness at
a low temperature, and the residue crystallised from absolute
alcohol.

Obtained in this manner, carminic acid forms a purple-brown
mass which gives a scarlet powder on trituration. It is with diffi-
culty soluble in ether, easily in water and alcohol.

It is a weak dibasic acid, forming violet salts ; those with the
alkalies are easily soluble, with the earths and heavy metals they
are insoluble. The sodium salt may be crystallised ; the other
salts are amorphous.

On boiling with dilute acids, carminic acid is split up into
carmine-red, CuHigO^, and a sugar, CgHioOs. In general, car-

266 CHEMISTRY OF ORGANIC DYESTUFFS.

minic acid gives the same decomposition products as carmine-red.
If an ammoniacal solution is allowed to stand, a nitrogenous
compound is formed^ possessing totally different dyeing properties.
On a large scale this product is prepared for dyeing by maceration
of ground cochineal with ammonia, and is used under the name of
ammoniacal cochineal.

In dyeing, this product gives much bluer shades, and is used for
modifying cochineal scarlets.

Carmine-red.
C11H12O7.

Carmine-red is prepared from the lake obtained by precipitating
a cochineal decoction with lead acetate. This lead lake is dis-
solved in dilute sulphuric acid, freed from lead by sulphuretted
hydrogen, and boiled with very dilute sulphuric acid for some
hours. Barium carbonate is added till a violet coloration ensues,
and then filtered rapidly and precipitated with lead acetate. The
lead lake is decomposed and the filtrate evaporated to dryness in
vacuo.

Carmine-red is a dark red substance, which appears green by
reflected light. It is insoluble in ether, but soluble in water and
alcohol with a red colour, lieducing agents convert it to a colour-
less compound. On fusion with potash carminic acid yields coccinin
[80] , and on heating with water to 200° ruficarraine is formed [82] .

By boiling carminic acid with nitric acid, trinitrococcussic acid
(trinitrocresotinic acid),

/OH
GrHa^COOH,

=(N02)

is formed [78] .

Bromine reacts with carminic acid, producing two brominated
compounds, a-bromcarmine, CioH4Br403 [81], forms colourless
needles, M.P. 248°, which are soluble in alkalies. On boiling with
strong potash solution it yields oxybromcarmine, which behaves
like an oxyacid of the formula

OTT
CsH4BrA<cooH ^^^^'

DYESTUFFS OF UNKNOWN CONSTITUTION. 267

On oxidation with potassium permanganate, oxybromcarmine
yields an acid of the formula C9Ht;Br204, probably dibromoxy-
tolylformic acid, CyHsOBrjCOCOOH. Dibrommethoxylmethyl-
phthalic anhydride,

OCH3

CH3— CeBrg-CO^

/
-(

x^. .0

is also formed [81] .

^-bromcarmine, CijHgBrsO^, forms yellow needles, M.P. 232°,
and gives red dibasic salts with the alkalies.

On oxidation with potassium permanganate it yields dibrom-
oxymethylbenzoyldicarbonic acid,

r H OBr /^^^^

^^^^^^'<CO-COOH

and the above dibrommethoxymethylphthalic anhydride [81].

Ruficoccin, CmHioOg, is formed along with a compound of the
composition C32H00O13 by heating carmine-red with sulphuric acid
to 130-140° [82]".

Ruficoccin is a brick -red powder, sparingly soluble in water and
ether, easily soluble in alcohol. It dissolves in alkalies with a
brown colour. On distillation with zinc powder a hydrocarbon,
C,(;Hj2, is formed [82].

Ruficarmine [82J forms a carmine-red powder insoluble in
water, but easily soluble in alcohol.

Carmine-red is a dibasic acid, and forms salts similar to those of
carminic acid.

Coccinin, C14H12O5 [80], is formed on melting carminic acid or
carmine-red with potash. It forms yellow leaflets, insoluble in
water, but soluble in alcohol and alkalies. The alkaline solution
becomes oxidised on exposure to the air, the colour changing
through green to red. A solution of coccinin in concentrated
sulphuric acid gives a blue coloration on addition of manganese
dioxide.

Carmine. — This is a commercial product made from cochineal,
which is used by artists and for colouring confectionery, and also
as rouge. Carmine forms porous red masses, which are easily
rubbed to fine powder. It is insoluble in water and alcohol, but
dissolves completely in ammonia if free from adulteration with
kaolin, starch, &c.

268 CHEMISTRY OF ORGANIC DYESTUFFS.

The exact method employed for this preparation is unknown ;
various recipes are in vogue, according to which the essential
consists in precipitating an aqueous decoction of cochineal with
alum. According to the researches of Liebermann [83] carmine
contains about 3 per cent, of alumina and about the same quantity
of lime, and also about 20 per cent, of albuminoid matters.

As the lime and alumina dissolve in ammonia and cannot be
detected therein by the ordinary reagents, it is probable that a
peculiar lake of carmine-red is present, in which the albuminoids
play a part.

The colour of carmine, and especially that of its ammoniacal
solution, differ considerably from that of carmine-red.

The above ammoniacal solutions were formerly used as red ink.

Cochineal is employed in dyeing for production of scarlet shades.
Before the introduction of the red azo-dyestuffs cochineal was the
only material which could be used for scarlets, but recently, owing
to competition with the artificial dyestuffs, its use has greatly
diminished. Neither carminic acid nor carmine-red can be fixed
without mordant. The finest scarlet tones are obtained with the
tin lake of carminic acid, or probably of the carmine-red formed
by its decomposition.

In dyeing wool scarlet, the mordanting and dyeing operations
are generally carried out in one bath, the material being boiled
with ground cochineal and stannous chloride, an addition of tartar
or oxalic acid being generally made. Yellower shades are obtained
by addition of weld, fiavine, or fustic.

The alumina lake has violet colour, and the iron a blackish- grey.
Owing to the latter, it is important to have water mordants, &c.,
perfectly free from iron in dyeing cochineal scarlet.

Ammoniacal cochineal produces bluer shades on tin mordants.
Cochineal is seldom used in cotton-dyeing. Cochineal lakes are
often used in printing, being mixed with albumen and fixed by
steaming. The artists' colour known as Florentine lake is prepared
by precipitating a decoction of cochineal with alum and soda or
chalk. It contains the alumina lake of carminic acid, mixed with
excess of alumina and chalk.

DYESTUFFS OF UNKNOWN CONSTITUTION. 269

LaC'dye.

Lac-dye is also a product of a species of Coccus, the Coccus
lacca or C. ficus. These insects live on the branches of Ficus
religiosa and Ficus indica. A resinous matter exudes from the
tree and envelopes the insects. The twigs are cut off along with
the resin, and sold as stick-lac. On treating stick-lac with water,
the colouring-matter dissolves, and the residue, melted and squeezed
through calico, forms commercial shellac. The exact method by
which commercial lac-dye is prepared is kept secret, but it probably
consists in precipitation of an alkaline decoction of stick-lac with
alum.

The colouring-matter contained in lac-dye was long considered to
be identical with that of cochineal, but, as shown by the researches
of R. E. Schmidt [95], it is a new body, laccainic acid, CigHijOg.

Lac-dye is used in dyeing in a similar manner to cochineal, the
principal diflcrence being that it requires a very acid bath. The
shades produced are not so clear as those of cochineal, but surpass
the latter in fastness both to light and alkalies.

Kermes, another insect [Coccus ilicis, C. baphia), contains
analogous colouring-matters, and was formerly used in dyeing,
but has now gone out of use.

Other insects, for example Coccus polonicus, C.fragarice, contain
red dyestuffs.

Colouring-matter of Tyrian Purple [84, 85].

Certain molluscs [Purpura lapillus, P. hcemastoma, and various
species of Murex), when crushed and exposed to sunlight, develop
a purple dyestuff which was highly prized by the ancients.
According to Schunck [84] the dyestuff, punicine, is insoluble in
water, alcohol, and ether, slightly soluble in benzene and glacial
acetic acid, and easily soluble in aniline and concentrated sul-
phuric acid [85]. It sublimes with partial decomposition in
leaflets, which have a metallic lustre,

Witt regards this dyestuff as indigo mixed with a red dyestuff
less fast to light. On ancient purple cloth this red has been
bleached in course of time, and only the blue-indigo ground
remains. Compare Witt [98] .

270 CHEMISTRY Of ORGANIC DYESTUFFS,

Catechu.

The commercial products known as Catechu and Cutch are
prepared by evaporation of aqueous extracts of the wood of Acacia
catechu and allied species, common in India. Gambier is a similar
preparation ; its exact composition has not been investigated.
Catechu serves technically both as a colouring-matter and as a
tannin, and is largely employed in cotton-dyeing and in tanning.

The principal constituents of catechu are catechin and catechu-
tannic acid.

Catechin. — On treating catechu with cokl water, catechu-tannic
acid dissolves, and the catechin contained in the residues may be
obtained by extraction with boiling-water. Catechin separates
from the solution on cooling, and may be purified by recrystal-
lising from boiliug-water. It forms minute white needles, M.P.
217°, which are sparingly soluble in cold water, readily in alcohol
and in boiling-water. Catechin yields pyrocatechin and phloro-
glucin on heating with dilute sulphuric acid under pressure. It
does not precipitate solutions of gelatine, tartar-emetic, or alka-
loids, thus differing from the tannins.

There is some uncertainty as to the exact composition of
catecbin. Liebermann and Tauchert give the formula

C21H20O9 + 5H2O

as most probable, and they have also analysed a dlacetyl com-
pound, M.P. 128°-130°, which supports this formula [105].

Etti ascribes to catechin the formula CsgUggOie, and uses this in
the following series of anhydrides described by him [106] .

By the action of heat, or of dilute acids, catechin gives rise to a
series of anhydrides. The first of these, catechn-tannic acid,
C38H34O15, is a natural constituent of catechu. This compound,
and the dianhydride CggHgoOi^, and the trianhydride CggHgoOis,
precipitate gelatine, and have a resemblance to the true tannins.
Further heating gives rise to the production of a fourth anhydride,
catechuretin, CasHsgOis, a compound insoluble in water.

Catechin reacts with two molecules of diazobenzene chloride,
producing a catechinazobenzene.

On oxidation with potassium bichromate, catechin yields
japonic acid, a reddish- brown compound, the chromium or copper

DYESTUFFS OF UNKNOWN CONSTITUTION. 271

lake of which is probably formed in tlie ordinary methods of
dyeing with catechu.

Catechu-tannic Acid. — This body, also known as catcchin-red,
is obtained by extracting catechu with cold water, or by heating
catechin with water to 110°. It precipitates gelatine but not
tartar-emetic, and gives a green coloration with ferric acetate.

It yields a reddish-brown compound on oxidation with potas-
sium bichromate, probably identical with the japonic acid formed
on oxidation of catechin.

Catechu is principally used in cotton-dyeing. It gives yel-
lowish shades on goods mordanted with aluminium or tin salts ;
but its main application is for the production of brown shades,
M"hich are very fast. The goods are steeped in a solution of
catechu and passed through a bath of potassium bichromate, to
which copper sulphate is sometimes added. The brown may
also be developed by airing or ageing. In calico-printing, catechu
may be fixed by one of the methods used for aniline black. A
mixture of catechu, potassium chlorate, and sal-ammoniac is
printed, and the colour developed by steaming.

Cacliou de Laval [97].

The above dyestuff, also known as Fast Grey, is a commercial
product prepared by melting various organic substances (sawdust,
bran, &c.) with sodium sulphide.

These products, discovered by Croissant and Bretonni6re, contain
peculiar weak acid dyestuffs, which contain sulphur.

Cachou de Laval dyes unmordanted cotton from an alkaline bath,
producing brownish shades, which are capable of modification by
passage through baths of various metallic salts (copper and iron,
chromium salts). In spite of its very unpleasant smell, it has an
extensive application in cotton- dyeing.

The shades are very fast to soap. Like canarin and the direct
dyeing tetrazo-colours, Cachou de Laval is capable of fixing basic
dyestuffs, and the shades can thus be topped at will.

By fusing sodium acetate with sulphur, E. Kopp obtained a sub-
stance closely resembling Cachou de Laval in its properties.

REFEEENCES.

The references are divided into tlie following sections : —

1. Introduction.

2. NiTHO-COMPOUNDS.

3. azo-compounds.

4. oxyquinones and qtjinoneoximes.
6. Ketoneimides and Hydbazides.

6. Triphenylmethane Dyestuffs.

7. QUINONEIMIDE AND AziNE DyESTUFFS.

8. Aniline Black, Indullnes and Nigrosines.

9. QtriNOLINE AND ACBIDINE DyESTUFFS.

10. Indioo Dyestuffs.

11. EuxANTHic Acid, Galloflavine, Canarine, and Mueexide.

12. Dyestuffs of unknown Constitution.

ABBREVIATIONS.

Ber. = Berichte der deutschen chemischen Gesellschafb zu Berlin.

Annal. = Annalen d. Chemie und Pharmazie (now Liebig's Annalen).

Journ. f. pr. Chem. = Journal f iir practische Chemie.

Jahresb. = Jahresbericht iiber die Fortschritte d. Chemie (Giessen : Ricker,

publisher).
Friedl. = Dr. P. Friedlander : * Fortschritte der Theerfarbenfabrication,' 1877-

1887 and 1887-1890 (Berlin : Julius Springer, publisher, 1888 and

1891).

INTRODUCTION.

[1] Runge, Poggendorffs Annal. xxxi. pp. 65 & 512 ; Reichenbach, Schweiger's

Journal f. Ch. Ixviii. p. 1.
[2] Natanson, Annal. xcviii. p. 297.
[3] Hofmann, Jahresb. 1858, p. 351.
[4] Renard freres et Franc, Brev. d'invent. of 8th April, 1859, and five

additional patents.
[5] Gerber-Keller, Brev. d'invent. of 29th October, 1859.
[G] Medlock, Brit, patent of 18th January, 1860 ; Nicholson, Brit, patent of

26th January, 1860.

274 CHEMISTRY OF ORGANIC DYESTUFFS.

[7] Girard et de Laire, Brev. d'invent. of 26th May, 1860.
[8] Brev. d'invent. of 10th December, 18G1.
[9] Kolbe and Schmitt, Annal. cxix. p. 169.
[10] Nicholson, Monit. scientif. vii. p. 5 ; Brev. d'invent. of 10th July, 1862.
[11] Monnet et Dury, Brev. d'invent. of 30th May, 1802.
[12] Wanklyn, Brit, patent, November 1862.
[13] A. W. Hofmann, Compt. rend. liv. p. 428, Ivi. pp. 945 & 1033, Ivii.

p. 1131 ; Jahresb. 1862, p. 428 ; Zeitsch. f. Ch. 1803, p. 393.
[14] Usebe,Brev. d'invent. of 28th October, 1862.
[15] Lightfoot, Brit, patent, 17th January, 1863; Brev. d'invent. 28th January,

1863.
[16] Martius and Griess, Zeitsch. f. Ch. ix. p. 132.
[17] Caro and Griess, Zeitsch. f. Ch. x. p. 278.
[18] Caro and Wanklyn, Journ. f. pr. Ch. c. p. "49.
[19] Keisser, Brev. d'invent. 18th April, 18GG.
[20] Girard, de Laire, and Chappotot, Brev. d'invent. 21st March, 18C0,

16th March, 1867.
[21] Hofmann and Girard, Ber. ii. p. 447.
[22] Rosenstiehl, Bull, de 1. Soc. industr. de Mulhouse, 1869.
[23] Ber. ii. p. 14.

[24] Hofmann and Geyger, Ber. v. p. 526.
[25] Hofmann, Ber. vi. p. 352.
[26] E. and 0. Fischer, Ann. cxciv. p. 274,
[27] Germ, patent of 15th December, 1877, No. 1886.
[28] Ber. ix. p. 1035.
[29] E. and 0. Fischer, Ann. ccvi. p. 130.
[30] Doebner, Ber. xi. p. 1236.
[31] Germ, patent. No. 11857, of 19th March, 1880; Brit, patent, 1880,

No. 1177.
[32] Witt and Koechlin, Germ, patents. No. 16916 and No. 1958 ; Brit, patents,

1881, No. 1373 and No. 5249.
[33] Caro and Kern, Amer. patents, 25th December, 1883, 22nd April, 8th July,

and 2nd December, 1884.

NITRO-COMPOUNDS.

[1] Laurent, Annal. xliii. p. 219.

[2] Schmitt and Glutz, Ber. ii. p. 52.

[3] Schunck, Ann. xxxix. p. 6, Ixv. p. 234.

[4] Piccard, Ber. viii. p. 685.

[5] Martius and Wichelhaus, Ber. ii. p. 207.

[6] Martius, Zeitschr. f. Ch. 1868, p. 80.

[7] Darmstiidter and Wichelhaus, Annal. clii. p. 299.

[8] Germ, patent, No. 10785, of 28th December, 1879; Friedl. i. p. 327.

[9] Lauterbach, Ber. xiv. p. 2028.

REFERENCES. 275

[10] Merz and Weith, Ber. xv. p. 2714.

[11] Gnehm, Ber. ix. p. 1245.

[12] niasiwetz, Annal. ex. p. 289.

[13] Schering, Germ, patent, No. 15117 and No. 15889.

AZO-COMPOUNDS.

[1] Liebermann, Ber. xvi. p. 2858.

[2] Zinke, Ber. xviii. p. 3132.

[3] Zinke and Bindewald, Ber. xvii. p. 3026.

[4] Spiegel, Ber. xviii. p. 1479.

[5] Gries8 and Martins, Zeitschr. f. Ch. 1866, p. 132.

[6] Kekul^, Zeitschr. f. Ch. 1866, p. 688.

[7] Janowsky, Ber. xix. p. 2157.

[8] Graessler, Germ, patent. 4186 ; Friedl. i. p. 439.

[9] Griess, Ber. xv. p. 2183.
[10] Griess, Ber. x. p. 528.
[11] Witt, Chemikerzeit. 1880, No. 26.
[12] Witt, Ber. xii. p. 259.
[13] Nietzki, Ber. x. pp. 662, 1155.
[14] Noelting and Witt, Ber. xii. p. 77.
[15] Nietzki, Ber. xiii. p. 472.
[16] Noelting and Forel, Ber. xviii. p. 2681.
[17] Hofmann, Ber. x. p. 213,
[18] Witt, Ber. x. p. 656.
[19] Mixter, Amer. Chem. Journ. v. p. 282.
[20] Nietzki, Ber. xvii. p. 345.

[21] Lippmann and Fleissner, Ber. xv. p. 2136, xvi. p. 1415.
[22] Noelting, Ber. xviii. p. 1143.
[23] Annal. bcxv. p. 74.
[24] Annal. cxxxv. p. 164.

[25] Caro and Griess, Zeitschr. f. Ch. 1867, p. 278.
[26] Buckney, Ber. xi. p. 1453.
[27] A. W. Hofmann, Ber. x. p. 28.
[28] Griess, Annal. cxxxvii. p. 60.
[29] Weselsky and Benedikt, Ber. xii. p. 228,
[30] Perkin and Church, Annal. cxxix. p. 108.
[31] Griess, Annal. cliv. p. 211.
[32] Kekul^ and Ilidegh, Bt^r. iii. p. 234.
[33] Kimmich, Ber. viii. p. 1026.
[34] Wallach and Kiepenheuer, Ber. xiv, p. 2617.
[35] Baeyer and Jaeger, Ber. viii. p. 148,
[36] Grie'ss, Ber. xi. p. 2192.
[37] Witt, Ber. v. p. 2196.
[38] Jaeger, B er. viii. p. 1499.

276 CHEMISTRY OF ORGANIC DYESTUFFS.

[39] Liebermann and Kostanecki, Ber. xviii. pp. 130 t& 882.

[40] Wallach and Schutze, Ber. xv. p. 3020.

[41] Mazzara, Gaz, chim. It. ix. p. 424.

[42] Noelting and Kolm, Ber. xvii. p. 351.

[43] Nietzki, Ber. xvii. pp. 344 & 1350.

[44] Griess, Ber. xvii. p. 608.

[46] Meister, Lucius, and Briining, Germ, patent, No. 3229, of 24th April,

1878; Brit, patent, 1878, No. 1715, Friedl. p. 377.
[40] WaUach, Ber. xv. p. 2825.
[47] Germ, patent. No. 6411, of 12th March, 1878; Brit, patent, 1878, No. 786 ;

Friedl. p. 358.
[48] Brit, patent, 1881, No. 2030 ; Friedl. p. 373.
[49] Griess, Ber. xiv. p. 2032.
[50] Griess, Ber. x. p. 627.
[51] Brit, patent, 1880, No. 4091.
[52] Stehbins, Ber. xiii. p. 716.
[53] Frankland, Joum. of Ch. Soc. xxxvii. p. 747.
[54] Brit, patent, 1881, No. 1767 ; FriedL i. p. 324.
[55] Germ, patent, No. 22707, of 9th September, 1882 ; Friedl. p. 539.
[56] Griess, Ber. ix. p. 627.
[57] Griess, Ber. xvi. p. 2028.

[68] Germ, patent, No. 22714, of 8th November, 1882 ; Friedl. i. p. 453.
[59] Caro and Schraube, Ber. x. p. 2230.
[60] Nietzki, Ber. xiii. p. 1838.

[61] Brit, patent, 1881, Nos. 1225, 2030 ; Friedl. p. 364.
[02] Joum. of the Chem. Soc, November 1883, March 1884.
[63] Witt, Brit, patent, 1883, No. 2237; Friedl. i. p. 391.
[64] Germ, patent, No. 28753, of 27th February, 1884 ; Friedl. i. p. 470.
[65] Paul, Germ, patent, No. 28820, of 13th December, 1883 ; Friedl. p. 447.
[66] Brit, patents, 1884, Nos. 9162, 9606; Friedl. i. p. 465.
[67] Brit, patent, 1883, No. 6767 ; Friedl. i. p. 562.
[68] Cassella, Brit, patent, 1885, No. 9214 ; Friedl. i. p. 451.
[69] Farbenfabr. Bayer and Co., Brit, patent, 1885, No. 3803; Friedl. i.

p. 473.
[70] Farbenfabr. Bayer, Brit, patent, 1885, No. 14424 ; Friedl. i. pp. 488-491.
[71] Schultz, Ber. xvii. p. 463.

[72] Roussin and Poirrier, Brit, patent, 1878, No. 4490 ; Friedl. i. p. 531.
[73] Meister, Lucius, and Briining, Brit, patent, 1878, No. 1715.
[74] Griess, Ber. xiii. p. 1956.
[75] Glaus and Oehler, Ber. xv. p. 312.
[76] Baeyer and Duisberg, Bsr. xx. p. 1426.
[77] Weinberg, Ber. xx. pp. 2906 & 3363.

[78] Germ, patent. No. 38735, of 29th January, 1886 ; Friedl. i. p. 510.
[79] Bender and Schultz, Ber. xix. p. 3237.
[80] A. G. Green, Joum. of Chem. Ind. 1888, p. 108 ; Ber. xxii. p. 968 ; Dahl

REFERENCES. 277

and Co., Germ, patent, No. 47012, of 8th June, 1888; Pfitzinger,
Gattermann, and Jakobsen, Ber. xxii. pp. 830, 422,580, 1063 ; (Erica) :
Engl, patent, 1888, No. 17333 ; 11. Anscliiitz and G. Schultz, Ber. xxii,
p. 683.
[81] Engl, patent, 1888, No. 6319.

OXYQUINONES AND QUINONEOXIMES.

[1] Kochleder, Annal. Ixxx. p. 324.

[2] Schunck, Annal. Ixvi. p. 176 ; Jahresb. 1855, p. 666.

[3] Graebe and Lieberniann, Ann. Suppl. vii. p. 300 ; Ber. ii. pp. 14, 332, 505,
iii. p. 359.

[4] Baeyer and Caro, Ber. vii. p. 972.

[5] Schunck, Jahresb. 1874, p. 446.

[6] Schutzenberger, ' Farbstoffe ' (Berlin, 1870), ii. p. 114.

[7] Baeyer, Ber. ix. p. 1232.

[8] Diehl, Ber. xi. p. 187.

[9] Perkin, Jahresb. 1874, p. 485.
[10] Stenhouse, Annal. cxxx. p. 343.
[11] Perger, Journal f. pr. Ch. xviii. p. 184.
[12] Graebe and Lieberniann, Annal. clx. p. 144.
[13] Wiedemann, Ber. ix. p. 856.
[14] Brit, patent. No. 1936, of 25th June, 1869.
[15] Perkin, Brit, patent, No. 1948, of 26th June, 1869.
[16] Meister, Lucius, and Briining, Jahresb. 1873, p. 1122.
[17] Perkin, Ber. ix. p. 281.

[18] Rosenstiehl, Bullet, de la Soc. chim. xxvi. p. 03.
[19] Schunck and Homer, Ber. xii. p. 584.
[20] Strecker, Annal. Ixxv. p. 20.
[21] De Lalande, Jahresb. 1874, p. 486.
[22] Vogel, Ber. ix. p. 1641.
[23] Lepel, Ber. ix. p. 1845 ; x. p. 159.
[24] Auerbach, Jahresb. 1874, p. 488.
[25] Perkin, Jahresb. 1873, p. 450.

[26] Schunck and Homer, Ber. ix. p. 679, x. p. 1823, xiii. p. 42.
[27] Caro, Ber. ix. p. 682.

[28] Prudhomme, Bullet, de la Soc. indust. de Mulhouse, xxviii. p. 62.
[29] Graebe, Annal. cci. p. 333.
[30] Journ. of the Chem. Soc. xxxv. p. 800.
[31] Brit, patent, 1881, No. 3603 ; Friedl. i. p. 168.
[32] Fitz, Ber. \iii. p. 631.
[33] Kostanecki, Ber. xx. p. 3133.
[34] Fuchs, Ber. viii. pp. 625 & 1026,

[35] Liebermann and Kostanecki, Ber. xviii. p. 2138.
[36] Jakobsen and Julius, Ber. xx. p. 2588.
[37] Kostanecki, Ber. xx. p. 3143.

278 CHEMISTRY OF ORGANIC DYESTUFFS.

[38] HofFmann, Ber. xviii. p. 46.

[39] Brit, patent, 1884, No. 2269 ; Friedl. i. p. 335.

[38 a] Graebe, Ber. xxiii. p. 3739 ; Rob. E. Schmidt, Joum. f. pract. Ch. xliii.

p. 237 ; Gattermann, Journ. f. pract. Ch. xliii. p. 246 ; Engl, patent,

1890, Nos. 8725, 12715, 17712, 18729.
[39 a] Engl, patent, 1884, No. 2269.
[40] R. E. Schmidt and Gattermann, Journ. f. pract. Ch. xliv. p. 103 ; Engl.

patent, 1888, Nos. 14353, 15121.
[41] Seuberlich, Ber. x. p. 38.
[42] R. E. Schmidt, Joum. f. pract. Ch. xliii. p. 232.

KETONEIMIDES AND PIYDRAZIDES.

[I] Brit, patents, 1884, Nos. 5512, 6741 ; Caro and Kern, Amer. patents,

December 25th, 1883, April 22nd, July 8th, December 2nd, 1884 ;

Friedl. i. p. 99.
[2] Michler, Ber. ix. p. 716.

[3] Brit, patent, 1886, No. 120022 ; Friedl. p. 94 ; Ber. xix., Ref. p. 889.
[4] Fehrmann, Ber. xx. p. 2844.
[5] Graebe, Moniteur scientif. 1887, p. 600.
[6] Ziegler and Locher, Ber. xx. p. 834.
[7] Graebe, Ber. xx. p. 3260.
[8] Engl, patent, 1885, No. 9858.

TRIPHENYLMETHANE DYESTUFFS.

[1] Brit, patents, 1884, Nos. 6512, 5741 ; Caro and Kern, Amer. patents, Decem-
ber 25th, 1883, April 22nd, July 8th, December 2nd, 1884 ; Friedl. i.
p. 99.

[2] Bottinger, Ber. xii. p. 975.

[3] E. & O. Fischer, Ber. xi. p. 950, xii. pp. 796 & 2348.

[4] 0. Doebner, Ber. xi. p. 1236.

[5] O. Fischer, Annal. ccvi. p. 130.

[6] Brit, patent, 1878, No. 728 ; Friedl. p. 40.

[7] O. Fischer, Ber. xiv. p. 25^1.

[8] 0. Fischer and T. Ziegler, Ber. xiii. p. 672.

[9] Brit, patent, 1878, No. 4406 ; Friedl. p. 117.
[10] Brit, patent, 1879, No. 2509.

[II] Germ, patent. No. 4988, June 8tb, 1878.
[12] E. & 0. Fischer, Annal. cxciv. p. ,274.
[13] Dale and Schorlemmer, Ber. x. p. 1016.

[14] Germ, patent. No. 16750, February 8th, 1881 ; Friedl. i. p. 57.

[15] Ph. Greiff, Germ, patent. No. 15120, January 26th, 1881 ; Friedl. i. p. 49.

[16] Rosenstiehl, Annal. de Chim. & Phys. (5) viii. p. 192.

[17] Germ, patent. No. 16710, February 24th, 1881.

[18] Brit, patent, 1881, No. 1212 ; Friedl. i. p. 54.

[19] A. W. Hofmann, Ber. vi. p. 352.

REFERENCES. 279

[20] Greiff, Brit, patents, 1879, Nos. 2515, 4828,

[21] Brunner and Brandenburg, Ber. x. p. 1845, xi. p. 697.

[22] O. Fischer and Koerner, Ber. xvii. p. 98.

[23] Fischer and Germaner, Ber. xvi. p. 706.

[24] E. Fischer, Ber. xii. p. 798.

[25] 0. Fischer and Koerner, Ber. xvi. p. 2904.

[26] A. W. Hofmann, Ber. xviii. p. 767.

[27] Lange, Ber. xviii. p. 1918.

[28] Hofmann, Compt. rend. 11 v. p. 428, Ivi. pp. 1033 & 945, Ivii. p. 1131 ;

Jahresb. 1862, p. 347.
[29] Victor Meyer, Ber. xiii. p. 2343.
[30] Brit, patents, 1877, No. 373] ; 1879, No. 2828.
[31] Caro and Graebe, Annal. clxxix. p. 203.
[32] Hofmann and Girard, Ber. ii. p. 447.
[33] Hofmann, Ber. vi. p. 263.
[34] Beckerhinn, Jahresb. 1870, p. 768.
[35] Schiitzenberger, ' Matieres color.,' Paris, 1867, i. p. 506.
[36] Girard, de Laire, and Chappotot, Zeitschr. f. Ch. 1867, p. 236.
[37] Girard and de Laire, Jahresb. 1862, p, 696.
[38] Hofmann, Jahresb. 1863, p. 417.
[39] Hofmann, N. Handworterbuch d. Ch. i. p. 626.
[40] Bulk, Ber. v. p. 417.

[41] E. Kopp, KUnstl. Farbstoffe, pp. 319 & S20.
[42] Usebe, Joum. f. pr. Ch. xcii. p. 337 ; Lauth, Bullet, de la See. Chim. 1861,

p. 78 ; French patent, June 26th, 1861.
[43] Hofmann, Ber. iii. p. 761.
[44] Kolbe and Schmitt, Annal. cxix. p. 169.
[45] Nencki and Schmitt, Joum. f. pr. Ch. (2) xxiii. p. 549.
[46] Graebe and Caro, Ber. xi. p. 1350.
[47] Liebermann and Schwarzer, Ber. ix. p. 800.
[48] Dale and Schorlemmer, Annal. clxvi. p. 281, excvi. p. 77.
[49] Zulkowsky, Annal. cxciv. p. 119, ccii. p. 194 ; Ber. x. p. 1201.
[50] Caro and Wanklyn, Journ. f. pr. Ch. c. p. 49.
[51] Runge, PoggendorfTs Annal. xxxi. pp. 65 & 612.
[52] Persoz fils, Pelouze, Traits de Chimie.
[53] Guinon, Mamas, and Bonnet, Brev. d'invent. 1862.
[54] Reichenbach, Schweiger's Journ. f. Ch. Ixviii. p. 1.
[55] Liebermann, Ber. ix. p. 334.
[56] Hofmann, Ber. xi. p. 1456, xii. pp. 1371 & 2216.
[57] Doebner, Ber. xii. p. 1462, xiii. p. 610.
[58] Baeyer, Ber. iv. p. 662.
[69] Claus and Andreae, Ber. x. p. 1305.
[60] Gukassianz, Ber. xi. p. 1179.
[61] Rosicki, Ber. xiii. p. 208.
[62] Baeyer, Annal. ccii. p. 68.

280 CHEMISTRY OF ORGANIC DYESTUFFS.

[63] Baeyer, Annal. clxxxiii. p. 1.

[64] Hofmann, Ber. viii. p. 62,

[66] Baeyer, Ber. iv. pp. 457, 663.

[66] Buchka, Annal. ccix. p. 261.

[67] Ileichl, Dingl. Polyt. Journ. ccxxxv. p. 232.

[68] A. Kern, Germ, patent.

[69] Girard and de Laire, Jahresb. 1867, p. 963.

[70] L. Gattermann and Wichmann, Ber. xxii. p. 227.

[71] W. V. Miller and Plochl, Ber. xxiv. p. 1700.

[72] M. Nathanson and P. Miiller, Ber. xxii. p. 1888.

[73] Engl, patent, 1889, No. 3333.

[74] Ileumann and Rey, Ber. xxii. p. 3001.

[75] M. Ceresole, Engl, patents, 1887, No. 15374, 1888, No. 9600, 1889,

No. 2035.

[76] Engl, patent, 1889, No. 13217.

QUINONEIMIDE AND AZINE DYESTUFFS.

[1] Nietzki, Ber. xvi. p. 464.

[2] Bindschedler, Ber. xvi. p. 865.

[3] Bindschedler, Ber. xiii. p. 207.

[4] Witt, Ber. xii. p. 931.

[5] Wurster and Sendtner, Ber. xii. p. 1803 ; Wurster, Ber. xii. p. 2072.

[6] Wurster and Schobig, Ber. xii. p. 1809.

[7] Koechlin and Witt, Brit, patents, 1881, Nos. 1373, 5249 ; Friedl. i. p. 283.

[8] Witt, Journ. of Chem. Ind. 1882.

[9] Cassella, Germ, addit. patent, No. 15915 ; Friedl. p. 285.
[10] Schmitt and Andi'essen, Journ. f. pract. Ch. (2) xxiv. p. 435.
[11] Hirsch, Ber. xiii. p. 1909.
[12] Mohlau, Ber. xvi. p. 2846.
[13] Bernthsen, Ber. xvii. p. 611.
[14] Lauth, Ber. ix. p. 1035.
[15] Engl, patent, No. 3751.
[16] Bernthsen, Ber. xvi. pp. 2903 & 1025.
[17] Mohlau, Ber. xvi. p. 2728.
[18] Nietzki, Ber. xvii. p. 223.
[19] Koch, Ber. xii. p. 592.
[20] Engl, patent, 1880, No. 2906.

[21] Miilhauser, Germ, patent, No. 23291, 3rd January, 1883.
[22] 0. N. Witt, Ber. xii. p. 939.
[23] 0. N. Witt, Journ. Soc. Chem. Ind. 1882.
[24] Hofmann & Geyger, Ber. v. p. 526.
[25] Witt, Ber. xviii. p. 1119.
[26] Private communication.
[27] A. W. Hofmann, Ber. ii. p. 374.

[28] Perkin, Jahresb. 1859-1863; and Proc. of the Royal Soc. xxxv. p. 717.
[29] Meldola, Ber. xii. p. 2065.

REFERENCES. 281

[30] Liebermann, Ber. vii. pp. 247 & 1098.

[31] Weselsky, Aiinal. clxii. p. 273.

[32] II. Koeciiiin, Engl, patent, 1881, No. 4899 ; Friedl. i. p. 269.

[3^3] Weselsky and Benedikt, Wiener Monatshefte, i. p. 886 ; Ber. xiv. p. 530.

[34] Brunner and Kramer, Ber. xvii. p. 1817.

[35] Bindschedler and Busch, Eug. patent 1881, No. 939.

[30] Beruthsen, Annal. ccxxx. pp. 73 & 211.

[37] Witt, Ber. xviii. p. 1119.

[38] Witt, Ber. xix. p. 411.

[39] Bernthsen, Ber. xix. p. 2604 j Annal, ccxxxvi. p. 332.

[40] Witt, Ber. xix. p. 2791.

[41] Nietzki, Ber. xix. pp. 3017 & 3136.

[42] Witt, Ber. xix. p. 3121.

[43] Nietzki, Ber. xix. p. 3017.

[44] Julius, Ber. xix. p. 1365.

[45] Witt, Ber. x. p. 873.

[46] Wiener Monatsh., July 1884.

[47] Eng. patent, 1886, No. 43 ; Friedl. i. p. 254.

[48] R. Nietzki, Ber. x. p. 1157.

[49] Nietzki and Otto, Ber. xxi. p. 1590.

[50] Nietzki and Otto, Ber. xxi. p. 1598.

[51] Nietzki and Otto, Ber. xxi. p. 1736.

[52] Witt, Ber. xxi. p. 719.

[53] Eng. patent, 1888, No. 5852. i

[54] Eng. patent, 1886, No. 14283.

[55] Eng. patent, 1890, No. 3098.

[54a] R. Nietzki, A. Dietze, & Miickler, Ber. xxii. p. 3030.

[55 a] Nietzki and Miickler, Ber. xxiii. p. 720.

[56] Germ, patent, 1886, No. 40868.

[57] 0. Fischer and E. Hepp, Ber. xxi. p. 2620.

[58] Germ, patent, 1888, No. 49853.

ANILINE BLACK, INDULINES AND NIGROSINES.

[1] Lauth, Bullet, d. 1. Soc. chim. Dec. 1864.

[2] Castelhaz, Deutsche Industriez. 1874.

[3] Persoz, Deutsche Industriez. 1808.

[4] E. Kopp, Moniteur scientif. 1861, p. 79.

[5] Rich Meyer, Ber. ix. p. 141.

[6] Fritzsche, Jourij. f. pract. Chera. xxviii. p. 202.

[7] Lightfoot, Jahresh. 1872, p. 1076.

[8] Witz, Jahresber. 1877, p. 1239.

[9] Nietzki, Unpublished observations.
[10] Coquillon, Compt. rend. Lxxxi. p. 404.
[11] Nietzki, Ber. ix. p. 616.
[12] B. Kayser, Verb. d. Kgl. Gewerbemuseums z. Niimberg, 1877.

282 CHEMISTRY OF ORGANIC DYESTUFFS.

[13] Witt, and Thomas, Ber. xvi. p. 1102,

[14] Calvert, Lowe, Clifft, Eng. patent, June 11th, 18G0.

[J 5] Goppelsroeder, Jahresber. 1876, p. 702.

[16] Caro, Private communication.

[17] Nietzki, Ber. xvii. p. 223.

[18] Nietzki, Ber. ix. p. 1168.

[19] Lauth, Bull. d. 1. Soc. chim. Dec. 1864.

[20] Cordelot, Monit. scientif. vi. p. 669.

[21] Caro and Dale, Dingl. Journ. chx. p. 46-5,

[22] Martius and Griess, Zeitschr. f. Chem. 1866, p. 136.

[23] liofmann and Geyger, Ber. v. p. 472.

[24] V. Dechend and Wichelhaus, Ber. viii. p. 1609.

[25] Stiideler, Dingl. Journ. clxxvii. p. 395.

[26] Witt, Ber. xvii. p. 74.

[27] Witt and Thomas, Chem. Soc. Journ. 1883, p. 112.

[28] Kimmich, Ber. viii. p. 1028.

[29] Caro, Neues Ilaudwbrterb. d. Chem., Art. Indulin.

[30] Coupler, French patent. No. 77854.

[31] Justus Wolff, Chem. News, xl. p. 4.

[32] Kruis, Jahresb. 1874, p. 1217.

[33] Liechti and Suida, Wagner's Jahresber. 1884, p. 546.

[34] Nietzki, Ber. xi. p. 1094; Verb. d. Vereins z. Bef. d. Gewerbefleisses

Berlin, 1877.
[35] Fischer and Ilepp, Annal. cclvi. p. 263, cclxii. p. 237, cclxvi. p. 249.
[36] Meister, Lucius, and Briining, Engl, patent, 1888, No. 16325 ; Friedl. ii.

p. 195.
[37] 0. Fischer and E. Hepp, Ber. xxi. p. 2617; Ber. xxiii. p. 838.
[38] Chemikerzeitung, 1891.

[39] Dahl and Co., Germ, patent No. 36899, March 11th, 1886, Nos. 39763,
45803, 4.3008; Farbwerke, Meister, Lucius, and Briining, Germ, patent,
No. 50819.
[40] Oehler, Germ, patent, No. 533357.
[41] Meister, Lucius, and Briining, Germ, patent, No. 34515.
[42] O. Fischer and Hepp, Ber. xxi. p. 2621.
[43] C. Schraube, Eng. patent. No. 15259, October 23rd, 1888, and No. 6875 of

1890.
[44] Annal. cclvi. p. 240.
[45] O. Fischer and E. Hepp, Ber. xxiii. pp. 2789-2793.

QUINOLINE AND ACRIDINE DYESTUFFS.

[1] Jacobsen and Beimer, Ber. xvi. p. 1082.

[2] Hofmann, Jahresb. 1862, p. 351.

[3] Nadler and Merz, Jahresb. 1867, p. 512.

[4] Hoogewerff and van Dorp, Ber. xvii. Kef. p. 48.

[6] Williams, Chem. News, ii. p. 219.

REFERENCES. 283

[G] Jacobsen, Germ, patents 23962, December IGth, 1882 ; 23188, November

4th, 1882 ; Friedl. i. p. 101.
[7] Jacobsen and Eeimer, Ber. xvi. p. 2(504.

[8] Fischer and Rudolf, Ber. xv. p. 1500; Fischer and Besthom, Ber. xvi.
p. 68.

3] Fischer and Tauber, Ber. xvii. p. 2925.

)] Fischer and Bedall, Ber. xv. p. 684.

I] Ilofmann, Jahresber. 1862, p. 346: Ber. ii. p. 879.

i] Fischer and Koevner, Ber. xvii. p. 203.

J] Anschiitz, Ber. xvii. p. 434.

l] Renouf, Ber. xvi. p. 1304.

)] A. "VV. Ilofmann, Ber. xx. p. 5.

3] Illasiwetz and Gilm, Annal. Supl. ii. p. 191.

'] Weidel, Ber. xii. p. 410.

i] FUrth, Wiener Monatshefte, ii. p. 416.

3] Boedecker, Annal. xxiv. p. 228.

)] Biichner, Annal. Ixix. p. 40.

I] Oehler, Eng. pat. 1888, No. 9614.

2] Leonhardt and Co., Eng. patent, No. 17971, 1889 ; and English patent,
1890, No. 8243.

INDIGO DYESTUFFS.

Baeyer, Annal. Suppl. vii. p. 56 ; Baeyer, Ber. xv. p. 785.

Nenclci, Ber. vii. p. 1593, viii. p. 336.

Engler and Janeke, Ber. ix. p. 1411.

Nencki, Journ. f. pract. Chem. [2] xvii. p. 98.

Baeyer and Emmerling, Ber. ii. p. 680.

Baeyer and Caro, Ber. x. pp. 692 & 1262.

Morgan, Jahresb. 1877, p. 788.

Widmann, Ber. xv. p. 2547.

Lipp, Ber. xvii. p. 1072.

Ilofmann and Kouigs, Ber. xvi. p. 738.

Forrer, Ber. xvii. p. 984.

Baumann and Tiemann, Ber. xii. p. 1192, xiii. p. 415.

Bayer, Ber. xiv. p. 1741.

Bayer and Knop, Annal. cxl. p. 29.

Suida, Ber. xi. p. 584.

Erdmann, Journ. f. pract. Chem. xxiv. p. 11 ; Laurent, ibid. xxv. p. 4.34.

Baeyer, Ber. xi. p. 1228.

Friedlander and Ostermaier, Ber. xiv. p. 1921.

Baeyer, Ber. xiii. p. 2259.

Friedlander and Wleiigel, Ber. xvi. p. 2227.

E. V. Meyer, Ber. xviii. Ilef. p. 274 ; Journ. f. pr. Ch. (2) xxx. p. 467.

Baeyer, Ber. xii. p. 456.

Baeyer and Oekonomides, Ber. xv. p. 2093.

284 CHEMISTRY OF ORGANIC DYESTUFFS.

[24] Baeyer and Comstock, Ber. xvi. p. 1704.

[25] Gabriel, Ber. xvi. p. 518.

[26] Claisen and Shadwell, Ber. xii. p. 350.

[27] Baeyer, Ber. xv. pp. 60 & 746.

[28] Baeyer, Ber. xv. p. 775.

[29] Schunck, Phil. Magazine (4) x. p. 73, xv. pp. 29, 117, 183; Jaliresb.

1855, p. 660, 1858, p. 465.
[30] Fritsche, Annal. xliv. p. 290.
[31] Sommaruga, Annal. cxcv. p. 305.
[32] Schwarz, Jahresb. 1863, p. 657.
[33] Baeyer, Ber. xii. p. 1315.

[34] Crum, Berzelius Jaliresb. iv. p. 189 ; Berzelius, Berz. Jahresb. iv. p. 190.
[35] Dumas, Annal. xlviii. p. 257.
[36] Loew, Ber. xviii. p. 950.

[37] Germ, patent. No. 32238 of March 28th, 1884; Friedl. i. p. 145.
[38] Baeyer and Emmerling, Ber. iii. p. 514.
[39] Engler and Emmerling, Ber. iii. p. 885.
[40] Nencki, Ber. viii. p. 727, vii. p. 1593, ix. p. 299.
[41] A. Baeyer, Eng. patent, 1880, No. 1177, and Germ, patent, No. 11857,

March 19th, 1880; Friedl. i. p. 127.
[42] Glaser, Annal. cxliii. p. 326, cxlvii. p. 78, cliv. p. 137.
[43] Germ, patent, No. 19266, December 23rd, 1881 ; Friedl. i. p. 136 ; Eng.

patent 1882, No. 1266 ; Friedl. i. p. 140.
[44] Baeyer and Drewsen, Ber. xv. p. 2856.
[45] Baeyer and Drewsen, Ber. xvi. p. 2205.
[46] Eng. patent, 1882, No. 1453 ; Friedl. i. p. 141.
[47] Claisen, Ber. xiv. pp. 350, 2400, 2468.
[48] Meister, Lucius, and Briining, Eng. patent, 1882, No. 3216; Friedl. i.

p. 142.
[49] Germ, patent, No. 21592, 12th August, 1882 ; Friedl. i. p. 138.
[50] Gevekoht, Annal. ccxxi. p. 330 ; Germ, patent, No. 23785, 13th January,

1883 ; Friedl. i. p. 139.
[51] Baeyer and Bloem, Ber, xvii. p. 963.
[52] P. Meyer, Ber. xvi. p. 2261, Germ, patent. No. 25136, 2nd March, 1883 ;

No. 27979, 22nd December, 1883 ; Friedl. i. pp. 148 & 149.
[63] Kekule, Ber. ii. p. 748.
[64] Baeyer, Ber. xvi. p. 769.
[66] Baeyer, Ber. xvi. p. 2188.
[56] Baeyer, Ber. xv. p. 782.
[57] Compt. rend. xii. p. 639.
[68] Baeyer and Lazarus, Ber. xviii. p. 2637.
[59] Baeyer, Ber. xiii. p. 2264.
[60] Forrer, Ber. xvii. p. 975.
[61] Schunck, Mem. of Manchester Phil. Soc. (2) xiv. pp. 185-237 ; Ber. xii.

p. 1220.
[62] Liubawin, Journ. d. russ. Chem. Ges. xiii. p. 659.
[63] Schutzenberger, Jahresb. 1877, p. 611 ; Giraud's Jahresb. 1880, p. 686.
[64] E. Fischer, Ber. xix. p. 1563, xvii. p. 569.

REFERENCES. 285

EUXANTHIO ACID, GALLOFLAVINE, CANARIXE,
AND MUKEXIDE.

[1] Stenhouse, Annal. li. p. 423.

[2] Erdmann, Journ. f. .pr. Ch. xxxiii, p. 190.

[3] Baeyer, Annal. civ. p. 257.

[4] Graebe and Ebrard, Ber. xv. p. 1675.

[5] Schmidt, Annal. xciii. p. 88.

[0] Spiegel, Ber. xv. p. 1964.

[7] Graebe, Ber. xix. p. 2607.

[8] V. Kostanecki, Ber. xix. p. 2918.

[9] Wichelhaus and Salzmann, Ber. x. p. 1397.
[10] Graebe, Ber. xix. p. 2607.
[11] Bohn and Graebe, Ber. xx.p. 2327.

[12] Germ, patent, No. 37934, 20th April, 1886 ; Friedl. i. p. 567.
[13] Prochoroff and Miller, Dingl. Journ. ccliii. p. 130.
[14] Markownikoff, Journ. d. russ. Chem. Ges. 1884, p. 380.
[15] Lindow, ibid. 1884, p. 271.
[16] Liebig, Poggend. Annal. xv. p. 546.
[17] Prout, Annal. d. Chim. & Phys. xi. p. 48.
[18] Liebig and Wcihler, Annal. xxvi. p. 319.
[19] Fritsche, Annal. xxxii. p. 31 6.
[20] Beilstein, Annal. cvii. p. 176,
[21] Graebe, Annal. ccliv. p. 265.
[22] R. Bohn, Engl, patent. No. 8373, 20th May, 1889 ; Engl, patent. No. 9427,

28th June, 1869 ; Graebe and Eichengriin, Ber. xxiv. p. 967.
[23] Nencki and Siebert, Journ. f. pr. Ch. xxiii. pp. 147 & 538; Badische
Aniline and Sodafabrik., Engl, patent, 1889, No. 9429.

DYESTUFFS OF UNKNOWN CONSTITUTION.

[1] Chevreul, Annal. d. Chim. et Phys. (2) Ixxxii. pp. 53-126 ; Lemons de
Chimie a la teinture, ii. ; Journ. de Chimie M^dicale, vi. p. 157.

[2] Erdmann, Annal. xliv. p. 292.

[3] Hesse, Annal. cix. p. 332.

[4] Rammelsberg, Jahresb. 1857, p. 490.

[5] Reim, Ber. iv. p. 329.

[6] Buchka, Ber. xvii. p. 683.

[7] Halberstadt and Reis, Ber. xiv. p. 611.

[8] Hummel and Perkin, Ber. xv. p. 2344.

[9] E. Kopp, Ber. vi. p. 447.
[10] BoUey, Journ. f. pr. Ch. cliii. p. 351.
[11] Liebermann and Burg, Ber. ix. p. 1885.
[12] Benedict, Annal. clxxviii. p. 100.

286 CHEMISTRY OF ORGANIC DYESTUFFS.

[13] Dralle, Ber. xvii. p. 372.

[14] Buchka and Erck, Ber. xviii. p. 1138.

[15] Wiedemann, Ber. xvii. p. 194.

[16] Loewe, Fresenius Zeitscbr. xiv. p. 119

[17] Wagner, Journ. f. pr. Ch. li. p. 482.

[18] Illasiwetz and Pfaiindler, Annal. cxxvii. p. 353.

[19] Benedict, Ber. viii. p. 606.

[20] Koch, Ber. v. p. 285.

[21] Illasiwetz, Annal. cxii. p. 109.

[22] Zwenger and Drouke, Annal. Suppl. i. p. 267.

[23] Bolley, Annal. xxxvii. p. 101.

[24] Rigaud, Annal. xc. p. 283.

[25] Liebermann and Hamburger, Ber. xii. p. 1179.

[26] Rochleder, Jahresb. 1859, p. 523.

[27] Bolley, Annal. cxv. p. 54.

[28] Hlasiwetz and Pfaundler, Jahresb. 1864, p. 560 ; Stein, Jahresb. 1862,

p. 500.
[29] Stein, Journ. f. pr. Ch. Iviii. p. 309.
[30] Borntriiger, Annal. Ixxxii. p. 197.
[31] Hlasiwetz, Annal. xcvi. p. 123.

[32] Kane, Berz. Jahresb. xxiv. p. 505 ; Gelatly, Jahresb. 1858, p. 473.
[33] Schiitzenberger, Jahresb. 18G8, p. 774.

[34] Liebermann and Hcirmann, Annal. cxevi. p. 307. ,

[35] Smorawsk}^, Ber. xii. p. 1595.

[36] Moldenhauer, Annal. c. p. 180 ; Journ. f . pr. Ch. Ixx. p. 428.
[37] Rochleder, Zeitscbr. f. Chem. 1866, p. 002.
[38] Schiitzenberger and Paraf, Jahresb. 1861, p. 707; Bullet, de la Soc.

Chimique, 1801, p. 18.
[39] Schiitzenberger and Berteche, Bullet, d. Mulhouse, xxxv. p. 455 ; Jahresb.

1868, p. 776.
[40] Stenhouse, Annal. li. p. 423.
[41] Erdmann, Journ. f. pr. Ch. xxxiii. p. 190.
[42] Baeyer, Annal. civ. p. 257.
[43] Graebe and Ebrard, Ber. xv. p. 1675.
[44] W. Schmidt, Annal. xciv. p. 88.
[45] Spiegel, Ber. xv. p. 1964.
[46] Wichelhaus and Salzmann, Ber, x. p. 1397.
[47] Graebe, Ber. xix. p. 2607.
[48] Piccard, Journ. f. pr. Ch. 1861, p. 709.
[49] Mylius, Journ. f. pr. Ch. 1864, p. 546.
roO] Stein, Jahresb. 1867, p. 731.
[51] Etti, Ber. xi. p. 864.
[52] Piccard, Ber. vi. p. 884.
[53] Daube, Ber. iii. p. 609.
[54] Iwanow-Gajewsky, Ber. iii. p. 624.

REFERENCES. 287

[55] Kachler, Ber. iii, p, 713.

[56] Jackson, Ber. xiv. p. 485.

[57] Wackenroder, Berg. Jaliresb. xii. p. 277.

[58] Zeise, Annal. Ixii. p. 202.

[59] Husemanu, Annal. cxvii. p. 200.

[60] Kane, Annal. xxxix. p. 25.

[61] Robiquet, Annal. xv. p. 292.

[62] Dumas, Annal. xxvii. p. 147.

[63] Liebermann, Ber. -vii. p. 247, viii. p. 1649.

[61 a] Wartha, Ber. ix. p. 217.

[62 a] Scblieper, Annal. Iviii. p. 362.

[63 a] Malin, Annal. cxxxvi. p. 117.

[64] Luynes, Jahresb. 1864, p. 561.

[65] Leo Meyer, Jahresb. 1847, p. 784.

[66] Weyerniann and Hafely, Annal. Ixxiv. p. 226.

[67] Francbimont, Ber. xii. p. 14.

[68] Pelletier, Annal. Iviii. p. 27.

[69] BoUey and Wydler, Annal. Ixii. p. 141.

[70] Carnelutti and Nasini, Ber. xiii. p. 1514.

[71] Quadrat, Jahresb. 1851, p. 532.

[72] Weiss, Zeitscbr. f. Cbemie, 1865, p. 552.

[73] L. Meyer and Koebleder, Journ. f. pr. Ch. xxiv. p. 1.

[74] R. Kayser, Ber. xvii. p. 2228.

[75] Cloez and Guignet, Jahresb. 1872, p. 1068.

[76] Kayser, Ber. xviii. p. 3417.

[77] Schaller, Jahresb. 1864, p. 410; Zeitscbr. f. Chem. 1805, p. 140.

[78] Warren De La Rue, Annal. Ixiv. p. 1.

[79] Schiitzenberger, Jahresb. 1858.

[80] Hlasiwetz and Grabowsky, Annal. cxli. p. 329.

[81] Will and Leymann,Ber. xviii. p. 3180.

[82] Liebermann and van Dorp, Annal. clxiii. p. 105.

[83] Liebermann, Ber. xviii. p. 1975.

[84] Lacaze Duthiers, Wagner's Jahresb. 1860, p. 448.

[85] Schunck, Ber. xii. p. 1359.

[86] Perrins, Annal., Suppl. ii. p. 191.

[87] Fleitmann, Annal. lix. p. 60.

[88] Hlasiwetz u. v. Gilm, Annal., Suppl. ii. p. 191.

[89] Weidel, Ber. xii. p. 410.

[90] Fiirth, Wiener Monatshefte, ii. p. 416.

[91] Boedecker, Annal. xxiv. p. 228.

[92] Biichner, Annal. Ixix. p. 40,

[92] R. Meyer, Ber. xii. p. 1393.

[93] Liebermann and Roemer, Ber. xx. p. 2428.

[94] J. Schmid, Ber. xix. p. 1734.

[95] R. E. Schmidt, Ber. xx. p. 1285.

288 CHEMISTRY OF ORGANIC DYESTUFFS.

[96] Arnaud, Compt. rendus, cii. p. 1119.
[97] Witt, Ber. vii. pp. 1530 & 1746.
[98] Bizio, Ber. vi. p. 142.
[99] G. Schultz, Annal. ccii.
[100] C. Schall and Dralle, Ber. xxiii. p. 1433.

[105] Liebermann and Tauchert, Ber. xiii. p. 694 ; see also Neubauer, Annal.
xcvi. p. 337 ; Kraut and Delden, Annal. cxxviii. p. 285 ; Etti, Annal.
clxxxvi. p. 327 ; Schiitzenberger and Rack, Bullet, d. 1. Soc. Chim. iv.
p. 6 ; Hlasiwetz, Annal. cxxxiv. p. 118.
[106] Etti, Wiener Monatshefte, ii. p. 547.

APPENDIX.

NITRO-COMPOUNDS.

P. 25. Naphthol Yellow S.

The a-naphtlioltrisulphonic acid used in the manufacture of
naphthol yellow S has the constitutional formula :

SO.H

The free acid of naphthol yellow S is constituted according to
the formula :

SOJI

NO,

AZO-DYES.

P. 56. Chromotropes.

These colouring-matters are prepared by action of diazo-cora-
pounds on the cliromotrope acid (see p. 295). The commercial

290 CHEMISTRY OF ORGANIC DYESTUFFS.

brands are 2 R, 2 B, 6 B, 8 B_, and 10 B. They dye wool from an
acid bath ; the shades vary from a bright scarlet with 2 R to a
reddish violet with 10 B^ but are not fast to soap. More valuable
results are obtained when the chromotropes are applied in con-
junction with a mordant. Darker and faster shades are obtained
by boiling the goods dyed with these dyestuffs with salts of copper,
aluminium, and iron, and various shades of black are produced by
action of potassium bichromate. It has been found advantageous
to use the mordant after dyeing, the operation taking place in the
same bath. Chromotrope 8 B gives the best and fastest shade of
black. The property of combining with metallic mordants pos-
sessed by these dyestuffs is due to the presence of two hydroxyl-
groups in the peri position. Chromotropes 2 R, 2 B, and 6 B give
a red solution with concentrated sulphuric acid, 8 B and 10 B give
a blue solution.

Amidonaphtholsulphonic Acids.

Several of these acids are known, but only one, the 7 or G acid,
is of importance. It is prepared by action of caustic soda on
/3-naphthylaminedisulphonic acid G (from /3-naphtholdisulphonic
acid and ammonia) at about 260°. It may be diazotised, and
reacts M'ith diazo-compounds to produce azo-colours, which may
be diazotised and combined on the fibre with other amines and
phenols. (See below, under Tetrazo-colours.)

The reaction between tetrazo-compounds and y-amidonaphthol-
sulphonic acid may be effected in either alkaline or slightly acid
solution, and the products differ according to which condition
is observed. The exact reason for this behaviour has not been
explained. For example, in the preparation of diamine blacks R
and B, and diamine blue-black E, the combination of the tetrazo-
compound with fy-amidonaphtholsulphonic acid is effected in
alkaline solution, while in the cases of Diamine Violet and Fast
Red a slightly acid solution is used.

P. 60. The following Azo-dyes contain the groups necessary
theoretically for the formation of mordant-dyeing colours. In fact
they yield fast shades when applied in conjunction with a chromium
mordant. It may be remarked that Diamond Black (p. 66) belongs
to the same category.

APPENDIX.

291

Byestuff.

Diazotiaed Base.

Combined ivith

Diamond Yellow G. .
Diamoud Yellow R. .

Cloth Brown R

Cloth Brown G ....
Cloth Orange

M-ainidobenzoic acid.
0-auiidobenzoic acid.

Benzidine. I

" )

" I

Salicylic acid.
Salicylic acid.
1 mol. salicylic acid, 1 mol.

a-naphthoLulplionic

acid.
1 mol. salicylic acid, 1 mol.

^/ii-dioxynaphthalene.
1 mol. salicylic acid, 1 mol.

resorcin.

Azo Black
Naphthol Black B .

Kaphthol Black 3 B

Naphthol Black 6 B

P. 66. Several black dyes of the disazo class have recently
appeared in commerce, and the more important of these are given
here. In the list the diazo-compound of tlie first-named body is
allowed to react with the second, and the resulting amido-azo-
compound is diazotised and combined with the third constituent.

Blue-Black B I /3-uaphthylamiuesulphonic acid +a-napht:hylamine +

( ^-naphtholdisulphonic acid R.

J jS-naphlhylamine-y-disulphonic acid+a-naphtbylaruine

( +R acid.

I a-naphthylaminedisulphonic acid B + a-naphthyl-

( amine + R acid.

i a-naphthylaminedisulphonic acid (Dahl)+a-naphthyl-

I amine+R acid.

Neio Black i a-naphthylaminedisulphonic acid B -|- a - naphthyl-

Anthracite Black . , . . ( amine-fdiphenylmetaphenylenediamine.

Victoria Black \ Sulphanilic acid + a-naphthylamine + 1-8 dioxy-

( naphthalenesulphonic acid.

P. 69. a-Naphthylaminesul phonic Acids.

On nitration of «-naphthalene-sulphonic acid, or on sulphonation
of a-nitronaphthalene, a mixture of two acids is formed. These
are separated by taking advantage of the different solubilities of
their sodium salts in water.

The sparingly soluble sodium salt yields an a-naphthylamine-
sulphonic acid on reduction, which has the constitution expressed
by the formula :

NIL

SOJI

292 CHEMISTRY OF ORGANIC DYESTUFFS.

It is known as naphthalidiuesulphonic acid or simply as Laurent's
acid. It is used^ but not to any great extent, in the manufacture
of azo-colours. The more easily soluble sodium salt obtained above
yields a-naphthylaminesulphonic acid S (peri -acid) on reduction.
It has the constitution :

SOJI NH,

It has hitherto not been made use of in the preparation of
azo-dyes.

The preparation of these acids is described in British Patents
Nos. 15775 and 15782, 1885.

The Laurent acid is also formed by action of fuming sulphuric
acid on a-naphthylamine hydrochloride or on acet-a-naphthalide.

a-Naphthylaminedisulphonic A cids.

Certain of these acids are used in the manufacture of black
azo-colours. A mixture of acids is formed by sulphonation of
naphthionic acid with fuming sulphuric acid, and these are
separated by treating the calcium salts of the mixture with alcohol.
The calcium salt soluble in alcohol of 96 °/^ yields acid No. I., the
residue contains acids II. and III., of which II. is soluble in alcohol
of 85 °/q. Acid I. yields azo-colours of no value, and No. III. is
of greater importance than No. II. Germ. Pat. 41957, Sept. 4,
1886.

^-Najihthylaminedisulphonic Acids.

These acids are prepared by heating the corresponding ^S-naph-
tholdisulphonic acids with ammonia. Thus R acid yields R-amido-
acid and G-(7)-acid yields G-(7)-amido-acid. The G-amido-acid
is also obtained by sulphonation of yS-naphthylamine at 100-140°
with fuming sulphuric acid.

a-Naphtholdisulphonic Acids.

'I. Schollkopf acid. — a-naphthylaminesulphonic acid S [suprh)
is sulphonated, and the resulting disulphonic acid converted into

APPENDIX.

293

naphtholdisulphonic acid by the diazo-reaction. The Schollkopf
acid has the constitution

soji on

SOJI

(Brit. P. 1885, 15775-15782). It is used in the manufacture of
azo-dyes.

II. a-naphthol-e-disulphonic acid (Andresen acid). — The mixture
of disulphonic acids obtained by sulphonatiou of naphthalene is
nitrated and reduced. The sodium salts of the amidodisulphonic
acids obtained are treated with water. The more easily soluble
salt yields the Andresen acid by the diazo-reaction, the sparingly
soluble one corresponds to the Schollkopf acid.

The Andresen acid has the constitution

SOJI OH

SOJI

It yields azo-dyes of a pure bluish shade, and is, next to the
Nevile-Winther acid, the most important derivative of a-naphthol.

A peculiar property possessed by a-naphtholsulphonic acids
which contain hydroxyl- and sulpho-groups in the peri (r8)
position, is that they yield anhydrides by elimination of water, and
these anhydrides (called sultones) are frequently obtained in place
of the acids, on decomposing the diazo-compounds with boiling
water. Thus the naphtholsulphonic acid corresponding to
a-naphthylaminesulphonic acid S yields naphtho-sultone,

SO, 0

294) CHEMISTRY OF ORGANIC DYESTUFFS,

The Scliollkopf acid gives naplithosultone-sulphonic acid,

SO. 0

SOJI

while an isomer is obtained from the Andresen acid. (Literature :
G. Schultz, Ber, xx. p. 3162 ; H. Erdmann, Annalen, ccxlvii.
p. 344 ; Bernsthen, Ber. xxii. p. 3327 ; Armstrong & Wynne,
Proe. Chem. Soc. 1890, p. 125. Brit. Patents, 1885, 15775-
15782; 1888,4625, 5910.)

Dioxynaphthalenesulphonic Adds.

Several of these acids are used in the manufacture of azo-colours.

I. Dioxynaphthalenemonosulphonic acid S is prepared by
melting a-naphtholdisulphonic acid (Schollkopf ) with caustic soda,
and has accordingly the constitutional formula :

OH on

SOJI

Azo-fuchsine B.

Diazotoluene and dioxynaphthalenesulphonic
Acid S.

Azo-fuchsine G. Diazobenzenesulphonic acid and dioxy-
naphthalenesulphonic Acid S.

These two dyestuffs dissolve in water with a bluish-red colour,
and in concentrated sulphuric acid with a violet colour. Azo-
fuchsine B comes into commerce as a brownish-black powder,
azo-fuchsine G as a reddish-brown powder.

APPENDIX.

295

They produce magenta shades on wool and are recommended as
substitutes for acid magenta on account of their fastness to light
and the clearness of the shades obtained. They may also be used
for printing woollens prepared with alum and stannic chloride.
German Pat. 54116, Oct. 25, 1889.

Dioocynaphthalenedimlphonic Acid (Chromotrope Acid).

Naphthalene is sulphonated with fuming sulphuric acid at from
80°-180° according to the strength of acid employed. The tri-
sulphonic acid obtained has the constitution

SOJI

SO,H

It is nitrated and reduced, and the resulting amido-acid submitted
to the diazo-reaction whereby a-naphtholtrisulphonic acid or its
sultone is formed. This yields a dioxynaphthalenedisulphonic
acid (Chromotrope Acid) on fusion with caustic soda.

The chromotrope acid is constituted according to the formula :

SO,H

SOJI

Dyes from Benzidine and Analogous Bases.

In the Table on p. 72 several derivatives of ethoxybenzidine are
enumerated, and the reactions whereby this base is obtained are
described here. Diazobenzene chloride reacts with jo-phenolsul-
phonic acid, producing benzene-azo-paraphenolsulphonic acid, the
azo-chain taking up an ortho-position with regard to the hydroxyl-
group.

296 CHEMISTRY OF ORGANIC DYESTUFFS.

Accordingly the compound is constituted according to the
formula :

1 2 OH 1

SO3H 4

On heating with ethyl chloride or bromide and alcohol in
presence of alcoholic potash, an ether is formed. On reduction
■with stannous chloride or zinc-powder and caustic soda, the ether
undergoes an intramolecular change, a sulphonic acid of ethoxy-
benzidiue, of the constitution :

4 1 1 /OCoHg 3

NH2— CeH,— CfiHgrSOsH 6

NH2 4

is formed. This is heated with water under pressure to 170°, and
sulphuric acid splits off, forming ethoxy benzidine sulphate.

OC2H5
. NHg — C6H4 — ^eHsXj^jj

Ethoxybenzidine is used in the manufacture of a number of the
so-called diamine colours.

Toluyleuediaminesulphonic acid of the constitution

SO,H

may be diazotised. The tetrazo-compound reacts with amines
and phenols; the toluylene browns are combinations with two
molecules of a metadiamine.

In the Table on p. 74, cotton-yellow and salmon-red are
erroneously described as obtained from diamidodiphenylene.
They are derivatives of diamidodiphenylurea, but are prepared
indirectly.

APPENDIX.

297

Cotton-yellow is obtained by action of phosgene on two molecules
of amidobenzene-azo-salicylic acid, and has the formula :

CO[NH-C6H4-N=N-C6H3 . OH . COOIIJa.

Salmon-red is prepared in an analogous manner from amido-
benzene-azonaphthionic acid, and has the formula :

CO[NH-C6H4-N = N-CioH5NH2 . SOgHls-

Mimosa is prepared by action of ammonia on the diazo-compound
of primuline.

Mikado Colours. — The yellow-orange and brown dyestuffs known
under this designation are prepared by action of alkalies on para-
nitrotoluenesulphonic acid in presence of oxidizable substances,
such as arsenious acid, glycerine, phenols, tannic acids, &c. Brit.
Pat. 1888, 2664.

They are probably more or less impure azoxystilbenedisul-
phonic acids. They dye cotton directly from a salt bath and
give moderately fast shades.

The following Table comprises some of the most important
direct dyes of recent introduction.

Dyestuff.

Diazotised Base.

Comhiiied loith

{

1 mol. toluvlene-diamine-

Toluylene Orange

Benzidine. -|

sulphonic acid.
1 mol. 0-cresol-carbonic
acid.

Diamine Scarlet ....

2 mols. ^-naphthol y-disul-

phonic acid.
1 mol. phenol.

Diamine Scarlet R . .

■ 1

(

1 mol. /3-naphthol G-disul-
phonic acid. The pro-
duct is elhylated.

1 mol. -y-amidonaphthol-

Diamine Brown V . .

■ )

sulphonic acid.
1 mol. m-phenylenedia-
mine.

Thiazol Yellow 1
Clayton Yellow )

Dehydrothio toluidine-

Dehydrothiotoluidinesul-

sulphonic acid.

phonic acid.

Congo Brown G ^ R are prepared by action of diazotised sul-
phanilic acid and naphthionic acid respectively on the combination.

298 CHEMISTRY OF ORGANIC DYESTUFFS.

obtained from tetrazo-diphenyl with 1 mol. of salicylic acid and
1 mol. of resorcin.

Diamine Blue 6 G. — yS-naphthylaminedisulphonic acid diazo-
tised and combined with 1*2 amidonaphthol ether. The product
is diazotised and combined with /3-naphthol.

Benzo-grey. — Tetrazodiphenyl is combined with equal molecules
of salicylic acid and a-naphthylaminc, the product diazotised and
combined with a-naphtholsulphonic acid (Nevile and Winther).

Benzo-olive. — Is prepared similarly to the above; dioxynaphtha-
lenesulphonic acid S being substituted for the last-named com-
ponent.

Benzo-itidigo-blue. — The combination of benzidine with 1 mol.
a-naphthylamine is diazotised and combined with two molecules
of dioxynaphthalenesulphonic acid S.

OXYQUINONES AND QUINONE OXIMES.

P. 91. Alizarin-blue S has the composition expressed by the
formula :

Ci7H9N04-f2NaHS03
(H. Brunck and Graebe, Ber. 1882, vol. xv. p. 1783.)

TRIPHENYLMETHANE DYESTUFFS.

P. 110. Cyanine B is prepared by oxidation of the sulphonic
acids of meta-oxytetralkyldiamidotripheuylcarbinol. (Germ. Pat.
60961.)

It is a greenish-blue dyestuff, tolerably fast to soap and light,
and recommended as a substitute for indigo-extract.

P. 112. New Magenta. — This product is prepared commercially
by the synthetic process outlined on p. 112.

Anhydroformaldehyde-aniline, CgHg— N = CH2, is heated with a
mixture of orthotoluidine and its hydrochloride to 100°. Aniline
splits off, and diamido-ditolylmethaue

CH^x

APPENDIX. 299

CH3

\n tT /CH3

^CeHg/

is formed. On further heating with ortho-toluidine, hydrochloric
acid, and an oxidising agent, a third molecule of ortho-toluidine
enters into reaction, the " new magenta " being produced. It is
accordingly a salt of triamidotritolyl-carbinol,

r /^^n

New magenta is more easily soluble than ordinary magenta, and
dyes a somewhat bluer shade.

P. 128. Diphemjiamine blue. — This compound has long been con-
sidered, as triphenyljjararosaniline identical with that obtained by
phenylation of pararosaniline. Hausdorfer (Ber. xxiii. p. 1961)
has compared diphenylamine blue with triphenylpararosaniline,
and demonstrated their identity.

P. 130. New Green. — Is analagous to Victoria-blue, being the
condensation product of dimethylamidobenzophenone with a-
phenylnaphthylamine (Germ. Pat. 41756).

The commercial product is a paste. It is principally intended
for calico-printing, and gives yellowish- green shades.

P. 138. Aurotine is the sodium salt of tetranitrophenol-
phthalein, prepared by nitration of phenolphthalem in sulphuric
or acetic acid solution (Eng. P. 3441, 1889). It dyes wool
either from an acid bath or on a chromium mordant, pro-
ducing orange-yellow shades fairly fast to light and washing.

P. 142. Cyclamine. — On heating dichlorfluorescein with sodium
sulphide in aqueous solution, a thiodichlorfluorescein is formed.
This is converted into a tetraiodthiodichlorfluorescem by action
of iodine, and the sodium salt appears in commerce as cycla-
mine. It dyes bluish-red shades resembling those obtained with
phloxine. In general the thio-derivatives dye bluer shades than
the corresponding fluoresceins.

P. 143. Violamine {Fast acid violet), R ^ B.— These dyestuffs are

300 CHEMISTRY OF ORGANIC DYF.STUFFS.

obtained by action of ortbo- and para-toluidine respectively on
fluorescein-chloride. (Germ. Pats. 49057, 53300, 1889.)

The Violamines are used for wool and silk, and give shades
fast to alkalies and light.

QUINONEIMIDE DYESTUFFS.

P. 158. Thionine blue G 0. — This dyestufE is closely allied to
methylene blue, and its constitution is expressed by the formula :

CfiHg— N(CH3)2

• ^%, / .CH3
CeH3=N^C2H5

It is prepared by oxidation of diraethylparaphenylenediamine-
thiosulphonic acid (see Methylene Blue) -with ethyl-methylaniline,
and boiling the resulting insoluble green compound with zinc-
chloride solution. A leuco-compound is formed, and is converted
into dyestuff by oxidation. The commercial product forms a
reddish-brown powder.

Toluidine Blue. — This body is also an analogue of methylene
blue, the dimethylparaphenylenediamine-thiosulphonic acid being
oxidised with ortho-toluidine. The hydrochloride has the consti-
tution expressed by the formula :

C,H3-N(CH3),

^< >

CeHs — CH3
-^
NH . HCl

The commercial product is the sulphate and forms a dark green
powder, easily soluble in water forming a bluish-violet solution.
In dyeing, toluidine blue gives redder shades than methylene
blue.

Methylene Blue N, — This dyestuff is a recent member of the
series, and is obtained from ethyl -ortho-toluidine in the same
manner as methylene blue from dimethyl-aniline.

APPENDIX. 301

It dyes redder shades than methylene blue.
Its constitution is expressed by the formula :

CH,

C,,H.— NH . C.H,

/6AA2

Thiocarmine. — This compound is a sulphonic acid of the
methylene-blue series, and is obtained from ethylbenzylaniline-
monosulphonic acid. Thiocarmine is an acid dyestufF and pro-
duces very pure greenish shades of blue on wool, which are, how-
ever, not very fast to light.

(English Patents, 4596 and 19065, 1890.)

P. 161. — The oxyindamines and oxyindophenols (Fast Blue,
Gallocyanines, &c.) are characterised by the ease with which they
react with amines of the fatty and aromatic series, and certain
compounds resulting from such reactions have appeared in
commerce.

Cyanamines. — This name has been given to the compounds
resulting from the action of ammonia and amines in presence of
an oxidising agent on Fast Blue R. (A description of Fast Blue
R or Naphthol Blue occurs on p. 161.)

Ammonia-cyanamine has a greener shade than the original fast
blue ; the dimethylamine-cyanamine is more valuable on account
of its pure greenish-blue shade.

It has been demonstrated that the green shades of fast blue
contain one of these cyanamines ; the formation of which results
from the interaction of fast blue 11 with the dimethylparapheny-
lenediamine formed during the reaction. (Schlarb. Chem. Zeit.
1891, pp. 1281 and 1318; Witt. Ber. 1890, xxiii. p. 2247.)

P. 165. Delphine Blue and Gallic Indigo are sulphonic acids of
compounds obtained by heating gallocyanine with auilire and analo-
gous bases. The constitution of these bodies has not been deter-
mined; they are not simple anilides of gallocyanine, as a carboxyl-
group splits off during the reaction.

These dyestuffs arc employed in calico-printing, giving pure

302

CHEMISTRY OF ORGANIC DYESTUFFS.

blue shades when applied with chromium acetate. (Germ. Pat.
55942, Sept. 27, 1889 ; 50999, July 23, 1889.)

Wool Greys. — These dyestuffs are obtained by action of aniline
and analogous bases on the condensation-products of nitroso-
dimethyl- and diethyl-aniline on Schaeffer's j3-naphtholsulphonic
acid.

AZINE DYESTUFFS.

Fast Black. — The commercial product bearing this name is
obtained, by action of nitroso-dimethylaniline on meta-oxy-
diphenylamine. It contains the groups characteristic both of the
oxyindamines and the azines. It is a basic dyestuff, and is fixed
on cotton prepared with sumac and acetate of iron.

Malta Grey and Nigrisine are bodies of unknown constitution
prepared by heating nitrosodimethylaniliue hydrochloride in
aqueous or alcoholic solution.

Methylene Grey is a similar solution obtained by oxidation of
dimethylparaphenylene diamine.

(German Patent, 49446, Feb. 2, 1889.)

INDULINES AND NIGROSINES.

The simplest Induline of the naphthalene series, rosinduline
par excellence, is formed by heating benzene-azo-a-naphthylamine
with aniline in alcoholic solution under pressure. Rosinduline
base forms reddish-brown crystals, M.P. I98°-199°. Its consti-
tution is expressed, by the formula :

f'r.Hi

Accordingly the compound described on p. 205 is a phenyl-rosin-
duline.

APPENDIX.

303

On heating with hydrochloric acid, rosinduline yields ammonia
and rosindulone, a compound having the constitutional formula :

-N

I
CJl,

Some of the sulphonic acids of rosindulone are now pre-
pared commercially, and come into commerce as Rosindulines.

Rosinduline 2 B dyes wool bluish red from an acid bath.

Rosindulines 2 G and G produce orange-red and scarlet shades
respectively, and when dyed on silk, exhibit a fine yellow
fluorescence.

On heating benzene-azo-a-dinaphthylamine with aniline, naph-
thyl and isonaphthylrosindulines are formed.

Isonaphthylrosinduline has the constitution expressed by the
formula :

-N
I
C„H,

An anilide of isonaphthylrosinduline having the formula

C«H.N : C,„H

Ck,H,NH . CH

is formed along with phenylrosinduline when benzene-azo-a-naph-
thylamine is heated with aniline.

Naphthyl blue is probably a salt of a sulphonic acid of amido-
isonaphthylrosinduline, and naphthyl violet is a dyestufP of similar
character. They are principally intended for silk, on which they
show a red fluorescence.

(O. Fischer and E. Hepp, Annal. cclxii. pp. 237-2G4; H. v.
Perger, Mittheil. Techn. Gewerbemuseums, 1891, pp. 202-253.)

304 CHEMISTRY OF ORGANIC DYESTUFFS.

INDIGO.

A process in the preparation of indigo from the plant consists
in macerating the plants in water and subjecting the liquor to
the action of air in presence of ammonia. This '' ammonia
process ^' is said to give larger yields and a product of greater
purity.

Diacetylindigo.

On heating indigo blue with acetic anhydride, sodium acetate,
and zinc powder, a diacetylindigo white is obtained. On oxidation
with nitrous acid in presence of acetic acid, diacetylindigo blue is
formed. This compound forms small glittering red crystals, soluble
in benzene with a beautiful red colour. Its constitution is ex-
pressed by the formula :

/C0\^ /C0\

^C.H,0 ^ ^CH^O

Indigo disulphonic Acid.

The mechanism of the reactions involved in the synthetic process
for preparing this compound has been explained by Heymann
(Berl. Ber, 1891, p. 3066). The yellow solution resulting from the
action of the sulphuric anhydride on phenyl-glycine contains the
sulphonic acid of indoxyl-sulphuric ester. On dilution of this
solution, oxidation is effected by the sulphuric anhydride.

QUINOLINE AND ACRID INE DYESTUFFS.

Berberine.

Extensive researches on the constitution of berberine have been
made by W. H. Perkin, Jun. (Cliem. Soc. Journal, 1890, p. 991).
Berberine is allied to papaverine, hydrastine, and narcotine ; it is
a derivative of isoquinoline, and has probably the constitution
expressed by the formula : —

APPENDIX. 305

CHo . 0~C

O C CH

I I

CH3O— C C C CH
/ \ / - / \ /
CH3O— C C C Cj

' I I I I I

HC C N CH2

\ / ^ 1/ \ /

c c c

H H H

On oxidation with potassium permanganate, berberine yields the
following series of compounds, all containing the twenty carbon
atoms of berberine intact : —

Oxyberberine, M.P. 198-200° C20H17NO4.

Dioxyberberine CsoHiyNOg.

Berberal, M.P. 149° CgoHi^NOr.

Anhydroberberic acid, M.P. 237° CjoHnNOg.

Berberic acid, M.P. 177-182° C20H17NO9.

DYESTUFFS OF UNKNOWN CONSTITUTION.

Patent Fustine.

Some compounds bearing this name have appeared in commerce.
They are prepared by action of diazo-compounds on a decoction
of fustic. They are applied in the same manner as fustic.

Fisetin, Quercitin, and Rhamnetin.

Herzig (Monatshefte f. Chem. 1891, pp. 172, 177) has demon-
strated that a close relationship exists between these compounds,
and the formula) given on pages 254f-256 have to be modified. The
molecular weight of quercitin was determined, and from this and
analytical data the formula for quercitin appears to be CijHi^O;.
Rhamnetin is a monomethylquercitin. Quercitin is a hydroxy-
fisetin, and the formula proposed by Schmid for fisetin has to be
altered according. Analyses of fisetin, its acetyl, methyl, and
ethyl derivatives prove that the correct formula is CjuHjoOg. On
oxidation by air in alkaUne solution, fisetin yields resorcin and

306 CHEMISTRY OF ORGANIC DYESTUFFS.

protocatechuic acid, while quercitin under similar conditions
yields phloroglucin and protocatechuic acid, these results being in
accordance with the idea that quercitin is a hydroxyfisetin.

Orcein.
(Zulkowski & Peters, Monats. f. Chem. 1890, p. 227.)

A study of the process by which orcein is formed from lichens,
by action of ammonia and air, shows that three colouring-matters
are formed, viz., orcein, a yellow crystalline compound, and an
amorphous body resembling litmus.

Pure crystallised orcein is insoluble in water, ether, and benzene ;
soluble in alcohol, acetone, and acetic acid. Pure orcein possesses
nearly two hundred times the tinctorial power of orchil extract.

The composition of orcein is expressed by the formula
CggHg^NjO;, and its formation may be expressed by the equation

4 CyHgOs + 2NH3 + 60 = C28H24N2O7 + 7H3O.

The yellow compound has the formula CjiHigNOg, and is prob-
ably formed according to the equation

3 C7H802 + NH3-|-30=C2iHi9N05-l-4HO.

It was found that the formation of orcein from orcin is much
more rapid in presence of hydrogen peroxide; other oxidising
agents did not give favourable results.

No compound of the orcein class can be obtained from resorcin
by action of hydrogen peroxide and ammonia. From a mixture
of resorcin and orcin a mixed orcein, " Reso-orcei'n,'^ C20H20N2O7,
is formed.

ALPHABETICAL INDEX.

A.
Acid dyes, 14.
Acridine dyestuffs, 207.

orange, 216.

yellow, 216.

Aldehyde green, 128.
Alizarin, 82.

, Alkyl-, 83.

black, 81.

blue, 91.

blue OR, 90.

blue S, 298.

Bordeaux, 89.

brown, 89.

, Ohloro-, 83.

cyanine, 89.

dyeing, 86.

green S, 92.

mdigo blue S, 92.

, Nitre-, 87.

orange, 87.

red S, 83.

sulphonic acid, 83.

synthesis, 83.

yeUow, 61,245.

Alkannin, 263.
Amaranth, 56.
Amidoazobenzene, 35.

, Acetyl-, 37.

jS-naphtholdisulphonic acid

55.

disulphonic acid, 36.

monosulphonic acid, 36.

Amidoazonaphthalene, 43.
Auiidoazotoluenebenzene, 39.
Amidoazotoluenes, 39.
Amidoazoxylenes, 40.
Amidonaphtholsulphonic acids, 290.
Aniidooxjazobenzene, 46.
Annatto, 258.
Anthracene yellow, 92.
Anthracite black, 291.
Anthraflavic acid, 89.
Anthragallol, 89.

Anthrapurpurin, 88.
Anthraquinoline, 91.
Anthraquinone, 84.

, Dichloro-, 84.

disulphonic acids, 84.

dyes, 81.

monosulphonic acid, 84.

Archil, 260.

brown, 65.

Auramine, 98.

Aurantia, 26.

Aurin, 132.

Aurin-tricarbonic acid, 134.

Aurotine, 299.

Auxochromic groups, 13.

Azarin S, 75.

Azine dyes, 1(59.

Azine-green, 189,

Azoaniline, 41.

Azobenzeneazoparacresol, 66.

Azobenzenedimethylamidobenzoic - acid,

()0.
Azobenzene-a-naphthol, 53.

monosulphonic acid, 54.

Azobenzene-/i{-naphthoi, .54.

disulphonic acids, 55.

monosulphonic acids, 54.

Azobenzene salicylic acid, 61.

Azo-bkck,291.

Azo-bluo, 71, 73.

Azo-carraine, 205.

Azo-conipounds, 28.

Azodibenzenephenylenediamine, 65.

Azodibenzenetoluylenediamine, 66.

Azo -S - diamidobenzoic acid-y-benzene-

sulphonic acid, (U).
Azo-dyes application, 34.

from amidoazo-couipounds, 63.

from benzidine, 68.

manufacture, 34.

on fibre, 77.

Azofuchsine, 294.
Azonaphthalene /3-naphthol, 57.
disulphonic acids, 58.

308

INDEX.

Azonaphthalene monosulphonic acid, 57.

resorciu, 46.

;- salicylic acid, 61.

Azoorseilline, 72.
Azoplienine, 201.
Azopbenols, 45.
Azorubine, 58.
Azoviolet, 74.
Azyline, 42.

B.
Basic dyes, 14.
Basle blue, 188.
Benzaurine, 135.

Benzeneamidoazonaphtbalene, 43.
Benzenedisazobenzene )8-napbthol, 64.

disulpbonic acid, 64.

monosulphonic acid, 64.

Benzenetetrazobenzenephenol, 63.
Benzhydrol, 97.
Benzidine blue, 72.
Benzoazurines, 73, 74.
Benzo-black, 74.
Benzo-blue-black Q & E, 74.
Benzo-brown B, 74.
Benzoflavine, 216.
Benzo-grey, 298.
Benzo-indigo-lilne, 298.
Benzo-olive, 298.
Benzo-orange, 72.
Benzopurpurines, 72, 73.
Berberine, 212, 304.
Bismark brown, 42.
Bixin, 258.
Black, Alizarin, 81.

, Aniline, 192.

dyeing, 197.

, Anthracite, 291.

, Azo, 66, 295.

- — — , Benzo-, 74.

, Benzo-blue, 74.

, Brilliant, 66.

, Diamine, R, 72, 290.

, ^-, B, 73, 290.

, , Blue E, 73, 290.

, Diamond, 66.

, Fast, 302.

, Jet, R, 66.

, Naphthol, 291.

, Naphthylarainp, D,66.

, New, 291.

, Victoria, 291.

, Wool, 65.

Blue, Alkali, 127.

, Aniline, 126.

, Azo, 71, 73.

, Basle, 188,

, Benzidine, 72.

black B, 295.

, Cotton, 127.

, Delphine, 300.

, Diamine, 73, 298.

Blue, Diphenylamine, 128, 299.

, Fast, 161.

. Gallamine, 164.

, Meldola, 162.

, Methylene, 155, 300.

, Naphthol, 161.

, Napbtyl, 303.

, Night, 127.

, Nile, 163.

, Paraph enylene, 203.

, Phenylene, 149.

, Resorcin, 167.

, Toluidine, 3(X).

, Toluylene, 150.

, Victoria, 130.

, Water, 127.

Bordeaux, 56, 57.

B, 58.

extra, 72.

Brazilein, 253.

Brazilin, 252.

Brilliant azurine 5 G, 74.

black, 66.

Congo, 72.

purpurin, 73.

Brown, Archil, 65.

, Benzo, 74.

, Bismark, 42.

, Cloth, 291.

, Congo, 297.

, Diamine, 297.

, Toluylene, 296.

Oachou de Laval, 271.
Canarine, 247.
Carmine-red, 266.
Carminic acid, 265.
Carminnaphthe, 58.
Carotin, 260.
Carthamin, 262.
Catechin, 271.
Catechu, 270.

tannic acid, 271.

Chinese green, 264.
Chrome yiolet, 134.
Chromogens, 3.
Chromophors, 3.
Chromotropes, 289.
Chrysamine Q-, 71, 72.

R, 72.

Chrysanilines, 124, 212.
Chrysin, 259.
Chrysoidine, 40.
Chrysophenine, 74.
Chrysotoluidine, 124.
Citronine, 39.
Classification, 21.
Cloth brown, 291.

INDEX.

309

Cloth orange, 291.
Coccinines, 56, 57, 267.
Cocliiiieal, 265.
Colour, 1.
Ccerulein, 144.
Congo rod, 68, 72.

, BrilHant, G, 72.

Corinth, 72.

violet, 72.

Crocetin, 264.
Crocin, 264.
Crude products, 20.
Curaeneazoresorcin, 45.
Curcumin, 259.
Cyanamines, oOO.
Cyanine, 203.

B, 298.

Cyanosine, 142.
Cyciamine, 299.

Dehydrothiotoluidine, 75.
Delphine blue, 300.
Deltiipurpurin, 72, 73.
Developers, 76.
Diamidoazobenzene, 40.
Diamidoazotoluenes, 42.
Diamond yellow, 291.
Dichroines, 165.
Diisatogen, 224.
Dimethylamidoazobenzene, 37.

sulphonic acid, 37.

Dimethylamidobenzeneazobenzoic acid,

59.
Dimethylamidobenzoic acid-azobenzoic

acid, 60.
Dinitrocresol, 24.
Dinitronaphthol, 25.

sulphonic acid, 25, 289.

Dinitrosoresorcin, 93.
Dioxindol, 221.
Dioxyazobenzenes, 44, 45.

sulphonic acid, 45.

Dioxynaphthalene sulphonic acids, 294.
Dioxynaphthoquinone, 81.
Dioxytartaric acid, 101.
Diphenylaniine blue, 128, 299.
Diphenylrosaniline, 126.
Disazo dyestuffs, 62.
Dyeing (theories), 3.

EUagic acid, 245.
Eosin, 139.

ether, 140.

scarlet, 141.

Erica, 76.

Erythrosin, 141.
Ethoxybenzidino, 296.
Eupittonic acid, 133.
Eurhodines, 172.
Eurhodoles, 175.
Euxanthic acid, 243.
Euxanthone, 243.

Pjsetin, 254, 3a5.
Flavaniline, 210.
Flavin, 2.")4.
Flavopurpurin, 88.
Fluorescein, 139.

, Tetrabrom-, 139.

, Tetrabromodichlor-, 142.

, Tetrabromotetrachlor-, 142.

, Tetraiodo-, 141 .

Fluorescent blue, 167.
Fluorindine, 206.
Fuchsine, 118.
Fustic, 253.

, Young, 254.

Pustine, 305.

(srallacetophenone, 245.
Gallamine blue, 165.
Gallein, 144.
Gallic indigo, 300.
Gallocyanine, 16.3.
Galloflavine, 240.
Gambine, 95.
Girofle, 185.
Glycereins, 145.
Green, Acid, 110.

, Aldehyde, 128.

, Azine, 189.

, Azo, 116.

, Benzaklebyde, 107.

, Bindschedler's, 149.

, Brilliant, 109.

, Chinese, 264.

, Ethyl, 109.

, Fast, 94.

, Helvetia, 109.

, Iodine, 122.

.Light, 110.

, Malachite, 107.

, Methyl. 116.

, Methylene, 161.

, Naphthol, 95.

New. 299.

,' New' solid 3 B, 109.

, Victoria 3B, 109.

, Quinoline, 110.

, Solid, 109.

, Victoria, 109.

310

INDEX.

Grey, Fast, 271.

, Methylene, 302.

, Wool, 302.

Hsematein, 250.
Hsematoxylin, 250.
Helianthine, 38.
Heliotrope, 74.

Hexaetbylpararosaniline, 116.
Hexamethoxylaurin, 133.
Hexaniethoxylpararosaniline, 134.
Hexamethylpararosaniline, 115.
Hexaniethyl-rosaniline, 122.
Hexanitrodipheiiylamine, 26.
History, 17.
Hydrazides, 96.

Imidothiodiphenylimide, 158.
Indamines, 146, 149.
Indazine M, 188.
Indian yeUow, 242.
Indiglucine, 225.
Indigo, 219.

, ammonia process, 304.

, application, 228.

blue, 224.

carmine, 227.

, Chloro-, 226.

, Diacetyl, 304.

, Dibenzoy], 226.

dicarbonic acid, 229.

extract, 227.

purpurin, 230.

red, 230.

rubin, 230.

substitute, 251.

sulphonic acids, 227, 304.

, synthesis, 231.

white, 226.

Indigotin, 225.
Indoine, 229,
Indol, 219.
Indophenine, 222.
Indophenols, 151.
Indoxanthic ether, 224.
Indoxyl, 220.
Indoxylic acid, 221.
Induliues, 200, 302.

, application, 204.

, soluble, 203.

Isatic acid, 223.
Isatin, 222.
Isatogenic ether, 224.
Isopurpuric acid, 27.
Isopurpurin, 88.

Ketone-imides, 96.

Laccaic acid, 269.
Lac-dye, 269.
Lacmoid, 168.
Lakes, 15.
Lanuguinic acid, 5.
Leuco-compoimds, 2.
Litmus, 261.
Logwood, 250.
Lokaetin, 265.
Lokain, 264.
Lo-Kao, 264.
Lutecienne, 141.
Luteolin, 257.

M.
Maclurine, 253.
Magenta, 118.

, Acid, 121.

, New, 298.

residues, 124.

S, 121.

Mauvaniline, 124.
Mauveine, 190.
Mikado colours, 297.
Mimosa, 297.

Monophenylrosaniline, 125.
Mordant-dyeing. 15, 80.
Morin, 253.
Murexide, 248.
Muscarine, 162.

Naphthaquinoneoximes, 94.

Naphthazarin, 81.

Naphthol-azo-dyes, 46.

Naphthol black B, 2B, 6B, 291.

a Naphtholmonosulphonic acid, Nevile

and Winther, 49.

, Schaeffer, 49.

a Napbtholdisulphonic acid, Sehollkopf,

60,292.

6, 275.

trisulphonic acid, 289.

/3 Naplitholazobenzoic acid, 59.

)8 Naphthol disulphonic acid G-, 52.

E, 53.

monosulphonic acid crocein, 51.

F, 52.

Schaeffer, 52.

Naphthol yellow, 25, 289.

INDKX.

311

a Naphtho-Sultone, 293.

a Naphthylaiuine disulphonic acids, 292.

mouosulphonic acids, 69, 291.

l3 Naplithylamine disulphonic acids, 292.

luonosulphonic acids, 291.

Naphthyl blue, 303.
Neutral dyes, 14.
New black, 291.
Nigrisiue, 302.
Nigrosine, 200.
Nitrobromsalicylic acid, 26.
Nitro-compouuds, 23.
Nitrosonaphthols, 94.

Orange, Acridine, 216.

, Benzo-, G & E, 72.

, Orocein, 65.

G, 55.

I, 54.

II, 54.

Ill, 38.

IV, 38.

, Palatine, 26.

, Toluylene, G & E, 73.

Orcein, 261, 306.
Orchil substitute, 43.
Orcin, 261, 306.
Orcirufamin, 168.
Orcirufin, 168.
Orseilline, 43.
Oxazines, 161.
Oxindol, 221.
Oxy-azobenzene, 44.
Oxy-azobenzenetoluene, 45.
Oxyazo-coiupounds, 44.
Oxyindamines, 161.
Oxyindophenols, 161.
Oxyketone dyes, 245.
Oxyquinones, 80.
Oxythiodiphenylimide, 159.

Pararosaniline, 111.
Pararosolic acid, 132.
Pentamethylpararosaniliue, 115
Pentamethyh'osaniHne, 122.
Pentoxy-authraquinone, 90.
Phenazine, 169.

Pheuolazo-ineta-benzoic acid, 69.
Phenoldisazobenzene, 62.
Phenolphthalein, 138.
Phenosaffranine, 178, 181.

, Diazo-, 182.

, Ethyl-, 183.

, Methyl-, 183.

Phenylamidoazobenzene, 38.

sulphonic acid, 38.

Phenylhydrazides, 100.
Phloxine, 142.
Phthaleins, 136.
Phthalopheuoncs, 137.
Picrainic acid, 27.
Picric acid, 24.
Pittacal, 133.
Polchroinine, 76.
Ponceaux, 56, 57.
Primrose, 141.
Primuline, 75.
Printing, 16.
Prune, 164.
Purple, Ethyl, 116.

, Hessian N, 74.

Purpurine, 87.

, Benzo-, B, 4 B, 6 B, 10 B, 72, 73.

, Brilliant, 73.

, Delta-, 5 B & 7 B, 72, 73.

Purree, 242.
Pyronines, 143.
Pyrophthalone, 209.

Quercitin, 255, 305.
Quercitrin, 254.
Quinoline dyes, 207.
Quinone-imides, 146.

-oximes, 80.

Quinophthalon, 209.

Eed, Anisol, 57.

, Carmine-, 266.

, Congo, 68, 72.

, Cotton, 73.

, Diamine, 3B, 73.

, NO, 73.

, Fast, 72.

, Direct, 73.

, Fast, 57.

, Magdala, 189.

, Methylene, 160.

, Naphthylene, 74.

, Phenetol, 57.

, Quinoline, 208.

, St. Denis, 74.

, Salmon, 74, 297.

, Silk, .59.

, Toluylene, 176.

Eesazurin, 167.
Eesorcinazobenzoic acid, 59.
Eesorcin-benzein, 135.
Besorciudisuzobenzene, 63.

312

INUEX

Resorufamine, 168.
Resorufin, 165.
Rhamnetin, 256, 305.
Rhodamine, 142.

S, 143.

Roccelline, 57.
Rosamine, 135.
Rosaniline, 118.

, Acetyl, 123.

aldehyde compounds, 123.

base, 120.

benzoyl, 123.

, Diphenyl, 126.

dyes, 105.

, Hexamethyl, 122.

, Monophenyl, 125.

, Pentametbyl, 122.

sulphonic acids, 121.

, Tetrabrom-, 121.

, Tetraethyl, 122.

, Tetramethyl, 122.

tribenzyl-niethyliodide, 123.

, Triethyl, 123.

, Trimethyl, 122.

, Triphenyl, 126.

Rosazurines, 73.
Rose Bengal, 142.
Rosindulines, 205, 303.
Rosolic acid, 133.

dyes, 132.

Ruberytbric acid, 82.
Rubramine, 185.
Rnlicoccin, 267.
Rutin, 256.

Saffranine, 177.

, Pheno-, 178, 181.

, Tolu-, 185.

SaflPranol, 187.
Saffron substitute, 24.
Saffrosine, 141.
Santalin, 263.
Scarlet, Biebrich, 64.

■ , Brilliant, 69.

, Brilliant Crocein M, 65.

, Crocein, 3 B & 7 B, 65.

, Crystal, 58.

, Diamine, 297.

2 G, 55.

, Silk-, 59.

Styrogallol, 92.
Sulpbonazurine, 73.
Sun Gold, 26.
Yellow, 76.

Tannin lakes, 16.
Tartrazine, 100.

Tetraethylrosaniline, 123.
Tetramethyldianiidobenzophenone, 96.

chloride, 97.

Tetramethyldiamidotriphenylcarbinol,
106.

, Chlor-, 109.

, Nitro-, 108.

sulphonic acid, 109.

Tetramethylpararosaniline, 114.
Tetramethylrosaniline, 122.
Tetranitrodiphenol, 26.
Tetranitronaphthol, 26.
Tetrazo-dyes, 62.
Thiazines, 153.
Thiocarmine, 301.
Thiodiphenylamine, 153.
Thioflavine, 76, 77.
Thionine, 155, 300.
Thionol, 159.
Thionoline, 159.
Thiotoluidine, 75.
Toluidine blue, 300.
Toluylenediaminesulphonic acid, 296.
Toluylene orange, 297.
Triamidoazobenzene, 42.
Triamidotriphenylcarbinol, 111, 118.
Tribenzylrosaniline-methyliodide, 123.
Triethylrosaniline, 123.
Trimethylrosaniline, 122.
Trinitroeuxanthone, 244.
Trinitrophenol, 24.
Trioxyacetopbenone, 245.
Trioxy-anthraquinone, 87.
Trioxybenzoplienono, 245.
Triphenylmethane dyes, 102.
Triphenylrosaniline, 126.

sulphonic acids, 126, 127.

Tropiiolin II & 00, 38.

Y&O, 44.

000 No. 1, 54.

Turkey red, 86.
Turmeric, 260.
Tyrian purple, 269.

Valuation of dyestuffs, 15.
Vesuvine, 42.
Victoria-black, 291.

blue, 130.

green, 109.

yellow, 24.

Violamine, 299.
Violaniline, 124.
Violet, Acid, 114.

, Amethyst, 185.

, Azo-. 74.

, Chrome-, 135.

, Congo, 72.

, Crystal-, 115.

, Diamine, N, 72.

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Nietzki, Rudolf Hugo

Chemistry of the organic
dye stuffs

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